Pipe joint

ABSTRACT

An annular sealing material seals a pipe joint between a socket and a spigot. The sealing material includes a bulb part which is composed of a first bulb, a second bulb located closer to the inner side of the socket than the first bulb, and a narrow part present between the first and second bulbs. The first bulb is pressed against the inner circumferential surface of the socket. The second bulb is pressed against the outer peripheral surface of the spigot. The second bulb is inclined towards the pipe center from the first bulb in a natural state before it is provided between the socket and the spigot. The inner diameter of the second bulb is smaller than the outer diameter of the spigot in the natural state. The second bulb is extensible in the pipe diameter direction due to elastic deformation of the narrow part.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.14/022,299, filed on Sep. 10, 2013, which is a divisional of U.S.application Ser. No. 13/146,256, filed Jul. 26, 2011, now issued as U.S.Pat. No. 8,573,654, which is a U.S. National Stage application ofInternational Application No. PCT/JP10/50755, filed Jan. 22, 2010, whichclaims priority from Japanese Patent Application No. 2009-014838, filedJan. 27, 2009; Japanese Patent Application No. 2009-014836, filed Jan.27, 2009; Japanese Patent Application No. 2009-014835, filed Jan. 27,2009; Japanese Patent Application No. 2009-110223, filed Apr. 30, 2009;Japanese Patent Application No. 2009-116035, filed May 13, 2009;Japanese Patent Application No. 2009-117098, filed May 14, 2009;Japanese Patent Application No. 2009-119368, filed May 18, 2009;Japanese Patent Application No. 2009-138737, filed Jun. 10, 2009;Japanese Patent Application No. 2009-148148, filed Jun. 23, 2009;Japanese Patent Application No. 2009-209878, filed Sep. 11, 2009;Japanese Patent Application No. 2009-211170, filed Sep. 14, 2009;Japanese Patent Application No. 2009-234064, filed Oct. 8, 2009;Japanese Patent Application No. 2009-236788, filed Oct. 14, 2009; andJapanese Patent Application No. 2009-243942, filed Oct. 23, 2009; saidpatent applications hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a pipe joint, particularly to a pipejoint in which a spigot formed at an end of one pipe is inserted into asocket formed at an end of another pipe, the pipes being joined to eachother and made of, for example, ductile cast iron.

BACKGROUND OF THE INVENTION

A so-called slip-on detachment preventive pipe joint known as this kindof pipe joint is described in, for example, Japanese Patent Laid-OpenNo. 5-231570 (1993). In the pipe joint, a lock ring is attached to theinner circumference of a socket, and an annular sealing material made ofrubber is disposed to seal the pipe joint over the periphery between theinner circumferential surface of the socket and the outer peripheralsurface of a spigot. The sealing material includes a heel part held bythe socket and a bulb part compressed between the inner circumferentialsurface of the socket and the outer peripheral surface of the spigot togenerate a sealing surface pressure. The inner diameter of the bulb partis reduced towards the socket inner side, and the bulb part has asubstantially elliptical cross-section formed so as to project obliquelytowards the pipe center. A projection formed on the outer periphery ofthe distal end of the spigot is engaged with the lock ring to exhibit adetachment prevention function between the socket and the spigot.

In the pipe joint configured thus, when joining the pipes to each otherby inserting the spigot into the socket, the inner circumferentialportion of the bulb part is bent and deformed (diameter expansion)outward in the pipe diameter direction, while the projection of thespigot passes by the inner circumference of the sealing material towardsthe inner side of the socket.

After the projection of the spigot passes by the inner circumference ofthe sealing material, the bulb part is compressed between the outerperipheral surface of the spigot and the inner circumferential surfaceof the socket, so that a sealing surface pressure is obtained.

SUMMARY OF THE INVENTION

In the above-described known configuration, however, a large force isrequired to deform the bulb part so as to bend (diameter expansion)outward in the pipe diameter direction when the spigot is inserted intothe socket. Thus, a large insertion force (joining force) has to beapplied when the spigot is inserted into the socket.

An object of the present invention is to provide a pipe joint in which aspigot is inserted into a socket with a small insertion force (joiningforce).

Another object of the present invention is to efficiently attach asealing material in a satisfactory pressed state in a so-calledmechanical-type pipe joint.

Another object of the present invention is to eliminate the need for thecontrol of a tightening torque for a bolt and a nut pressing a pushring, bring a sealing material into surface contact with a socket and aspigot uniformly over a wide area to exhibit sealing properties, andmaintain desired sealing properties even if a part of the sealingmaterial contributing to the sealing properties moves in the pipe axialdirection, in a so-called mechanical-type pipe joint.

Another object of the present invention is to join pipes even with bentpipe axes while satisfactorily maintaining a detachment preventionfunction, and satisfactorily perform centering of a lock ring withoutcontrolling the orientation of a lock ring centering member.

Another object of the present invention is to reduce the weight and costof a pipe joint by making a liner disposed between the inner end of asocket and the distal end of a spigot arrangeable onto the axes of thesocket and the spigot.

Another object of the present invention is to effectively prevent theoccurrence of corrosion of a press claw and pipes in a detachmentpreventive pipe joint using the press claw.

Another object of the present invention is to prevent the diameterexpansion maintaining portion of a spacer from being misaligned with alock ring, when the diameter expansion maintaining portion of the spaceris inserted into a space between two ends of a constituent member at thedivided part of the lock ring, in a pipe joint in which the spacer isfitted in the divided part in the circumferential direction of the lockring provided in a socket to keep the lock ring in a diameter-expandedstate while a spigot is inserted into the socket.

Solution to Problem

A pipe joint according to a first aspect of the present invention inwhich a spigot formed at an end of one pipe is inserted into a socketformed at an end of another pipe, the one pipe and the other pipe beingjoined to each other,

the pipe joint comprising:

a fitting groove formed on the inner circumferential surface of thesocket; and

an annular sealing material for sealing a gap between the socket and thespigot over the periphery,

the sealing material including a heel part fitted into the fittinggroove, and a bulb part interposed between the inner circumferentialsurface of the socket and the outer peripheral surface of the spigot,closer to the inner side of the socket than the heel part,

the bulb part including a first bulb continuous with the heel part, asecond bulb positioned closer to the inner side of the socket than thefirst bulb, and a narrow part present on the boundary between the firstbulb and the second bulb,

the first bulb having a first sealing portion formed on the outerperipheral portion of the first bulb, the first sealing portion beingpressed against the inner circumferential surface of the socket,

the second bulb having a second sealing portion formed on the innercircumferential portion of the second bulb, the second sealing portionbeing pressed against the outer peripheral surface of the spigot,

wherein the second bulb is inclined from the first bulb towards a pipecenter in a natural state before the second bulb is provided between thesocket and the spigot, the inner diameter of the second bulb is smallerthan the outer diameter of the spigot in the natural state, and thesecond bulb is expansible and contractible in the pipe diameterdirection due to elastic deformation of the narrow part.

A pipe joint according to a second aspect of the present invention inwhich a spigot formed at an end of one pipe is inserted into a socketformed at an end of another pipe, the pipes being joined to each other,

the pipe joint comprising:

an annular sealing material interposed and compressed between the innercircumferential surface of the socket and the outer peripheral surfaceof the spigot to exhibit desired sealing properties; and

a push ring fastened to the socket to keep the sealing material in acompressed state in which the sealing material is interposed between theinner circumferential surface of the socket and the outer peripheralsurface of the spigot.

A pipe joint according to a third aspect of the present invention,

the pipe joint comprising a sealing material compressed between theouter peripheral surface of a spigot and the inner circumferentialsurface of a socket formed parallel to the outer peripheral surface ofthe spigot to exhibit desired sealing properties, wherein

the sealing material includes a cylindrical portion having an outerperipheral surface formed parallel to the inner circumferential surfaceof the socket and an inner circumferential surface formed parallel tothe outer peripheral surface of the spigot, and

the cylindrical portion is brought into surface contact with the outerperipheral surface of the spigot and the inner circumferential surfaceof the socket when the sealing material is compressed between the socketand the spigot.

A pipe joint according to a fourth aspect of the present invention,

the pipe joint comprising:

a lock ring accommodating groove formed on the inner circumference of asocket;

a lock ring accommodated in the accommodating groove and singularlydivided in a circumferential direction;

an annular centering member disposed between the inner circumferentialsurface of the accommodating groove and the outer peripheral surface ofthe lock ring, for holding the lock ring centered with respect to thesocket when a spigot is not inserted into the socket; and

a protrusion which is formed on the outer periphery of the distal end ofthe spigot, is capable of elastically pushing out the lock ringaccommodated in the accommodating groove with the spigot inserted intothe socket in the pipe diameter direction to pass through the innercircumference side of the lock ring, and is capable of being engagedwith the lock ring from the inner side of the socket when a detachmentforce is applied in the pipe axial direction between the socket and thespigot joined to each other to prevent the spigot from being detachedfrom the socket,

the centering member including a plurality of divided parts in the pipecircumferential direction, and a connecting part connecting the adjacentdivided parts in the pipe circumferential direction,

the divided part including a holder holding the lock ring from the outerperipheral side, and a hold width protruding inward in the diameterdirection from the socket inner side portion of the holder so as to beengaged with the lock ring in the pipe axial direction, wherein

the connecting part is disposed closer to the outer peripheral side thanthe divided parts and is elastically deformable in the pipe diameterdirection in response to the elastically pushed-out lock ring.

A pipe joint according to a fifth aspect of the present invention,

the pipe joint comprising:

a liner pushed into the inner side of a socket by a spigot and disposedbetween the distal end surface of the spigot and the inner end surfaceof the socket when the spigot is inserted into the socket; and

a guiding surface formed on the inner surface of the socket for guidingthe liner in the pipe diameter direction such that the axis of the lineris positioned at the axis of the socket and the spigot when the liner ispushed into the inner side of the socket by the spigot.

A pipe joint according to a sixth aspect of the present invention,

the pipe joint comprising:

a press claw disposed on the inner circumferential portion of a socket,or disposed on the inner circumferential portion of an annular memberfitted onto a portion of a spigot on the outer side of the socket andconnected to the socket; and

a press bolt for pushing the press claw to fix the press claw pressedagainst the outer surface of the spigot to the spigot, wherein

the press claw is made of an iron material and has an anticorrosivecoating formed on a surface of a portion in contact with the spigot, and

the anticorrosive coating contains any one of a Zn—Sn alloy sprayedcoating, a Zn—Sn—Mg alloy sprayed coating, and a Zn—Al alloy sprayedcoating.

A spacer according to the present invention for a pipe joint in which aspigot formed at an end of one pipe is inserted into a socket formed atan end of another pipe, the pipes being joined to each other,

an annular lock ring is accommodated in a lock ring accommodating grooveformed on the inner circumference of the socket, the lock ring includingdivided parts in the circumferential direction and being elasticallyexpansible in diameter,

a protrusion is formed on the outer periphery of the spigot, and

the protrusion of the spigot is allowed to pass through the lock ringhaving an expanded diameter, and the diameter-expanded state of the lockring is released after the passage of the protrusion,

the spacer being capable of being inserted into and removed out from thedivided part of the lock ring and maintaining the diameter-expanded lockring when the spacer is inserted into the divided part,

the spacer comprising:

a diameter-expanded maintaining portion being capable of being insertedinto and removed out from a gap between two ends of the lock ring alongthe circumferential direction at the divided part, and being interposedbetween the two ends when the maintaining portion is inserted; and

a handle reaching from the diameter-expanded maintaining portion outsidethe socket beyond a socket opening portion when the diameter-expandedmaintaining portion is interposed between the two ends of the lock ring,wherein

the spacer is capable of being removed out from the gap between the twoends of the lock ring at the divided part after the spigot is insertedinto the socket, passing through a space between the socket and thespigot and being collected outside the socket beyond the socket openingportion,

the spacer further comprises insertion grooves on two side portions ofthe diameter-expanded maintaining portion,

the two ends of the lock ring can be fitted into the insertion grooveswhen the diameter-expanded maintaining portion is inserted into the gapbetween the two ends of the lock ring at the divided part, and

the diameter-expanded maintaining portion is capable of being detachedin a removal direction from the two ends of the lock ring when thediameter-expanded maintaining portion moves to be removed out from thegap between the two ends of the lock ring at the divided part.

Advantageous Effects of Invention

According to the present invention, the sealing material including thefirst bulb, the second bulb, and the narrow part is provided, so thathigh sealing properties can be exhibited between the socket and thespigot as well as reducing an insertion force (joining force) requiredwhen the spigot is inserted into the socket.

According to the present invention, provided are the annular sealingmaterial interposed and compressed between the inner circumferentialsurface of the socket and the outer peripheral surface of the spigot toexhibit desired sealing properties, and a push ring fastened to thesocket to keep the sealing material in a compressed state in which thesealing material is interposed between the inner circumferential surfaceof the socket and the outer peripheral surface of the spigot. Thus, thepush ring can be efficiently attached without minutely controlling theinterval between the push ring and a flange. Accordingly, the operationefficiency can be improved and the sealing material can be easily keptin a favorable compressed state. As a result, the reliability of thepipe joint can be improved.

According to the present invention, the sealing material has acylindrical portion having an outer peripheral surface formed parallelto the inner circumferential surface of the socket, and an innercircumferential surface formed parallel to the outer peripheral surfaceof the spigot. The cylindrical portion is brought into surface contactwith the outer peripheral surface of the spigot and the innercircumferential surface of the socket when the sealing material iscompressed between the socket and the spigot. Thus, sealing propertiescan be maintained by bringing the sealing material into surface contactwith the spigot and the socket uniformly over a wide area. Further,desired sealing properties can be obtained even when the sealingmaterial receives a pressure in pipe to move a portion of the sealingmaterial exhibiting the sealing properties.

According to the present invention, the centering member includes aplurality of divided parts in the pipe circumferential direction and aconnecting part connecting the adjacent divided parts in the pipecircumferential direction. The divided part has a holder holding thelock ring from the outer peripheral side, and a hold width whichprojects inward in the diameter direction from the socket inner sideportion of the holder and is engageable with the lock ring in the pipeaxial direction. The connecting part is disposed closer to the outerperipheral side of the lock ring than the divided part and iselastically deformable in the pipe diameter direction in response to theelastically pushed-out lock ring. Thus, the lock ring can be reliablyprevented from being detached from the accommodating groove, and thedetachment preventive function can be satisfactorily maintained, toimprove the reliability of the pipe joint. Further, the lock ring can beelastically pressed inward in the diameter direction of the socket by areaction force of the elastically deformed connecting part. Thus, thelock ring can be satisfactorily centered by the centering member.

According to the present invention, when the spigot is inserted into thesocket, provided are the liner pushed into the inner side of the socketby the spigot and disposed between the distal end surface of the spigotand the inner end surface of the socket, and the guiding surface forguiding the liner in the pipe diameter direction such that the axis ofthe liner is located at the axis of the socket and the spigot when theliner is pushed into the inner side of the socket by the spigot. Theliner can be self-aligned, so that the outer diameter and thickness ofthe liner can be reduced according to the outer diameter and thicknessof the spigot. Thus, the liner can be reduced in weight and cost.

According to the present invention, the press claw pressed against theouter surface of the spigot by being pushed by the press bolt in theannular member and fixed to the spigot is made of an iron material, andcontains any one of a Zn—Sn alloy sprayed coating, a Zn—Sn—Mg alloysprayed coating, and a Zn—Al alloy sprayed coating on the surface of aportion in contact with the spigot, thereby exerting an excellentanticorrosive effect. Further, an anticorrosive effect due to a sprayedcoating can be expected even when the distal end portion of the pressclaw cuts into the spigot of the pipe. Thus, the occurrence of corrosioncan be effectively prevented in the press claw and the pipe.

According to the present invention, the spacer used for the divided partof the lock ring has insertion grooves on two side portions of thediameter-expanded maintaining portion. Two ends of the lock ring at thedivided part can be fitted into the insertion grooves when thediameter-expanded maintaining portion is inserted into a gap between thetwo ends of the lock ring. Further, the diameter-expanded maintainingportion can be detached in a removal direction from the gap between thetwo ends of the lock ring when the diameter-expanded maintaining portionmoves to be removed out from the gap between the two ends of the lockring at the divided part. Thus, the diameter-expanded maintainingportion of the spacer can be prevented from being displaced in thediameter direction and the insertion direction from the lock ring whenthe diameter-expanded maintaining portion of the spacer is inserted intothe divided part of the lock ring to keep the lock ring in adiameter-expanded state. Consequently, the diameter-expanded maintainingportion can be set at a normal position of the divided part of the lockring without being displaced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the essential part of a pipejoint according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a sealing material of FIG. 1.

FIG. 3 is an explanatory diagram showing the dimension of the sealingmaterial.

FIG. 4 shows the joining operation of the pipe joint of FIG. 1.

FIG. 5 shows the operating stage following the joining operation of FIG.4.

FIG. 6 shows the operating stage following the stage of FIG. 5.

FIG. 7 shows the operating stage following the stage of FIG. 6.

FIG. 8 is a vertical cross-sectional view showing the essential part ofa pipe joint according to another embodiment of the present invention.

FIG. 9 is an enlarged view showing the essential part of the part shownin FIG. 8.

FIG. 10 is a transverse cross-sectional view showing the essential partof the part shown in FIG. 9.

FIG. 11 shows the joining operation of the pipe joint of FIG. 8.

FIG. 12 shows the operating stage following the joining operation ofFIG. 11.

FIG. 13 shows the operating stage following the stage of FIG. 12.

FIG. 14 shows the operating stage following the stage of FIG. 13.

FIG. 15 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 16 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 17 shows the joining operation of the pipe joint of FIG. 16.

FIG. 18 shows the end surface of a socket flange in the pipe joint ofFIG. 16.

FIG. 19 is a front view showing a push ring in the pipe joint of FIG.16.

FIG. 20 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 21 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 22 shows a push ring and a sealing material in the pipe joint ofFIG. 21.

FIG. 23 shows the joining operation of the pipe joint of FIG. 21.

FIG. 24 shows the operating stage following the joining operation ofFIG. 23.

FIG. 25 shows a modification example of the pipe joint of FIG. 21.

FIG. 26 shows the joining operation in another modification example ofthe pipe joint of FIG. 21.

FIG. 27 shows the operating stage following the joining operation ofFIG. 26.

FIG. 28 shows the operating stage following the stage of FIG. 27.

FIG. 29 shows another modification example of the pipe joint of FIG. 21.

FIG. 30 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 31 shows a push ring in the pipe joint of FIG. 30.

FIG. 32 shows the joining operation of the pipe joint of FIG. 30.

FIG. 33 shows a method for inspecting the pipe joint of FIG. 30.

FIG. 34 shows a modification example of the push ring which can be usedin the pipe joint of FIG. 30.

FIG. 35 shows another modification example of the push ring which can beused in the pipe joint of FIG. 30.

FIG. 36 is a cross-sectional view showing the push ring of FIG. 35.

FIG. 37 shows a modification example of the pipe joint of FIG. 30.

FIG. 38 is a side view showing the essential part of the pipe joint ofFIG. 37.

FIG. 39 shows another modification example of the push ring which can beused in the pipe joint of FIG. 30.

FIG. 40 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 41 is a cross-sectional view showing a sealing material shown inFIG. 40.

FIG. 42 shows the joining operation of the pipe joint of FIG. 40.

FIG. 43 is an enlarged view showing a push ring in FIG. 42.

FIG. 44 is an enlarged view showing the sealing material in FIG. 42.

FIG. 45 shows a pipe joint according to another embodiment of thepresent invention.

FIG. 46 is an enlarged view showing the essential part of FIG. 45.

FIG. 47 is an overall side view showing a centering member of FIG. 45.

FIG. 48 is a three-dimensional view showing the centering member.

FIG. 49 shows the positional relationship between the centering memberand a lock ring.

FIG. 50 shows the joining operation of the joint of a pipe jointaccording to another embodiment of the present invention.

FIG. 51 shows the operating stage following the joining operation ofFIG. 50.

FIG. 52 shows the operating stage following the stage of FIG. 51.

FIG. 53 shows a modification example of the pipe joint of FIGS. 50 to52.

FIG. 54 shows a socket of the pipe joint of FIGS. 50 to 52 in anothermodification example.

FIG. 55 shows the joining operation of the joint of the pipe joint ofFIGS. 50 to 52 in still another modification example.

FIG. 56 shows the operating stage following the joining operation ofFIG. 55.

FIG. 57 is a three-dimensional view showing a liner centering member inthe pipe joint of FIG. 55.

FIG. 58 shows a modification example of the liner centering member ofFIG. 57.

FIG. 59 shows the joining operation of the joint of the pipe joint ofFIGS. 50 to 52 in still another modification example.

FIG. 60 shows the operating stage following the joining operation ofFIG. 59.

FIG. 61 is a cross-sectional view showing a pipe joint according toanother embodiment of the present invention.

FIG. 62 shows an example of a state of an anticorrosive coating formedon a press claw in the pipe joint of FIG. 61.

FIG. 63 shows another example of the state of the anticorrosive coatingformed on the press claw.

FIG. 64 shows still another example of the state of the anticorrosivecoating formed on the press claw.

FIG. 65 shows a modification example of the pipe joint of FIG. 61.

FIG. 66 is a cross-sectional view showing a pipe joint according toanother embodiment of the present invention.

FIG. 67 is a side view enlargedly showing the essential part of the pipejoint of FIG. 66.

FIG. 68 is a three-dimensional view showing a spacer which can be usedin the pipe joint of FIG. 66.

FIG. 69 is a plane view showing the spacer of FIG. 68.

FIG. 70 is a right side view showing the spacer of FIG. 69.

FIG. 71 is an enlarged view showing the essential part of the spacer ofFIG. 70.

FIG. 72 is a front view showing the spacer of FIG. 69.

FIG. 73 shows the essential part of the spacer of FIG. 72.

FIG. 74 is another drawing showing the essential part of the spacer ofFIG. 72.

FIG. 75 shows the joining operation of the pipe joint of FIG. 66.

FIG. 76 is a cross-sectional view showing the essential part of the pipejoint of FIG. 75.

FIG. 77 is a bottom view showing the spacer and the vicinity of thespacer in the pipe joint of FIG. 75.

FIG. 78 is a bottom view showing that the spacer is separated from alock ring accommodating groove in the pipe joint of FIG. 75.

FIG. 79 shows the diameter-expanded state of a lock ring before thespacer of FIGS. 68 to 78 is used.

DETAILED DESCRIPTION OF THE INVENTION

In a push-on detachment preventive pipe joint 11 of FIG. 1, a spigot 15formed at an end of one ductile cast-iron pipe 14 is inserted into asocket 13 formed at an end of another ductile cast-iron pipe 12, thepipes 12 and 14 being joined to each other.

On the inner circumferential surface of the socket 13, a fit-in groove17, a recess 18 located closer to the socket inner side than the fit-ingroove 17, and a lock ring accommodating groove 19 located closer to thesocket inner side than the recess 18 are formed across the periphery. Aprojection 20 is formed between the fit-in groove 17 and the recess 18.An inner end surface 21 is formed in the pipe diameter direction on thesocket inner side in the interior of the socket 13, away from the lockring accommodating groove 19.

The lock ring accommodating groove 19 accommodates a lock ring 22 whichis made of metal and singularly divided in the circumferentialdirection. The lock ring 22 has such an elastic diameter reducing forcethat the lock ring 22 is elastically pressed against the outerperipheral surface of the spigot 15. A centering rubber 23 is disposedbetween the outer peripheral surface of the lock ring 22 and the bottomsurface of the lock ring accommodating groove 19. The centering rubber23 facilitates the insertion of the spigot 15 into the lock ring 22, sothat the lock ring 22 can be held to be centered with respect to thesocket 13 when the spigot 15 is not inserted into the socket 13. Aprojection 24 is formed on the outer periphery of the distal end portionof the spigot 15, the projection 24 being engageable with the lock ring22 from the socket inner side. The projection 24 is formed in the pipeaxial direction at a predetermined distance from the distal end surfaceof the spigot 15. The projection 24 is engaged with the lock ring 22from the socket inner side, thereby preventing the spigot 15 from beingdetached from the socket 13.

An annular sealing material 25 made of rubber seals the pipe joint overthe periphery between the socket 13 and the spigot 15. The sealingmaterial 25 is configured as follows.

As shown in FIGS. 1 to 3, the sealing material 25 integrally includes ahard heel part 26 fitted in the fit-in groove 17 and a bulb part 27,which is softer than the heel part 26, interposed between the innercircumferential surface of the socket 13 and the outer peripheralsurface of the spigot 15. The heel part 26 is an annular member with arectangular traverse section.

The bulb part 27 is annularly formed and includes a first bulb 28 and asecond bulb 29 joined to each other. The traverse section of the firstbulb 28 is elliptically elongated in the pipe axial direction with twoends along the pipe axial direction each having a semicircular portionwith radius r1. The traverse section of the second bulb 29 iscircular-shaped with radius r2. Radius r1 is smaller than radius r2, andthickness t1 of the first bulb 28 along the pipe diameter direction issmaller than thickness t2 of the second bulb 29. The diameter (=2×r2) ofthe traverse section of the second bulb 29 is larger than space S in thepipe diameter direction between the inner circumferential surface of theprojection 20 and the outer peripheral surface of the spigot 15.

The first bulb 28 is joined to the heel part 26, and an annular recess31 is formed on the outer peripheral portion of the joint between thefirst bulb 28 and the heel part 26. Inner diameter K of the first bulb28 is slightly smaller than the outer diameter of the spigot 15, and theouter diameter of the first bulb 28 is slightly larger than the innerdiameter of the projection 20.

The first bulb 28 is located closer to the inner side of the socket 13than the heel part 26. A narrow part 32 is formed at the joint of thefirst bulb 28 and the second bulb 29, and the narrow part 32 is smallerin thickness than the first bulb 28 and the second bulb 29. On the innercircumferential surface and the outer peripheral surface of the narrowpart 32, annular recesses 33 and 34 with arc-like cross-sections areformed, respectively.

The second bulb 29 is located closer to the inner side of the socket 13than the first bulb 28, and is inclined from the first bulb 28 towardsthe pipe center. As shown in FIG. 3, a line containing center P1 of thesemicircular portion of the end of the first bulb 28 closer to thesecond bulb 29 and center P2 of the second bulb 29 is denoted as L1, aline containing the center P1 and extending along the diameter directionof the sealing material 25 is denoted as L2, and inclination angle N ofthe line L1 with respect to the line L2 is set to be 15° to 35°. Thesecond bulb 29 has an inner diameter (d) smaller than outer diameter D1of the spigot 15, and is expansible and contractible in the pipediameter direction due to the elastic deformation of the narrow part 32.Inner diameter J of the heel part 26 is larger than the inner diameter Kof the first bulb 28.

A first sealing portion 35 is formed in the pipe axial direction overthe outer periphery of the first bulb 28 so as to be pressed against theinner circumferential surface of the projection 20 of the socket 13. Asecond sealing portion 36 is formed over the inner circumference of thesecond bulb 29 so as to be pressed against the outer peripheral surfaceof the spigot 15. The first sealing portion 35 is not aligned with thesecond sealing portion 36 in the pipe axial direction. As shown in FIG.1, a gap 37 is present in the pipe diameter direction across theperiphery between the outer periphery of the second bulb 29 and thebottom surface of the recess 18 of the socket 13. The length of theprojection 20 of the socket 13 in the pipe axial direction is set suchthat the second bulb 29 is not compressed.

In the above configuration, when the other pipe 12 and the one pipe 14are joined to each other, first, the centering rubber 23 and the lockring 22 are accommodated in the lock ring accommodating groove 19. Asshown in FIG. 4, the heel part 26 of the sealing material 25 is fittedin the fit-in groove 17, so that the sealing material 25 is attachedinto the socket 13.

Next, the spigot 15 is inserted into the socket 13. At this point intime, as shown in FIG. 5, the distal end of the spigot 15 is insertedinto the inner circumference of the first bulb 28, is brought intocontact with the second bulb 29 and pushes the second bulb 29 in theinsertion direction. Thus, the second bulb 29 is elastically expanded(diameter expansion) in the pipe diameter direction.

After that, when the spigot 15 is inserted further into the socket 13,as shown in FIG. 6, the projection 24 of the spigot 15 passes by theinner circumference of the heel part 26 and is brought into contact withthe inner circumference of the first bulb 28. The first bulb 28 is theninterposed between the outer peripheral surface of the projection 24 andthe inner circumferential surface of the projection 20 of the socket 13,and is compressed in the pipe diameter direction. At this point, a gap38 is kept across the periphery between the outer periphery of thesecond bulb 29 elastically diameter-expanded in the pipe diameterdirection and the bottom surface of the recess 18.

When the spigot 15 is inserted further into the socket 13, as shown inFIG. 7, the projection 24 of the spigot 15 passes by the innercircumference of the first bulb 28, and is brought into contact with theinner circumference of the second bulb 29. At this point, since the gap38 is formed as shown in FIG. 6, the second bulb 29 can be displacedoutward in the pipe diameter direction to escape from the projection 24.

Thereafter, when the spigot 15 is inserted further into the socket 13,as shown in FIG. 1, after passing by the inner circumference of thesecond bulb 29, the projection 24 of the spigot 15 passes by the lockring 22 from the socket outer side towards the socket inner side whileelastically expanding the lock ring 22 in diameter. Thus, the other pipe12 and the one pipe 14 are joined to each other. At this point, thesecond bulb 29 is elastically expanded in the pipe diameter direction,so that the second bulb 29 sticks to the outer peripheral surface of thespigot 15. The diameter expansion of the second bulb 29 pushes the firstbulb 28 outward in the pipe diameter direction. Thus, the first sealingportion 35 of the first bulb 28 is pressed against the innercircumferential surface of the projection 20 of the socket 13, and thesecond sealing portion 36 of the second bulb 29 is pressed against theouter peripheral surface of the spigot 15, so that high sealingproperties can be obtained between the socket 13 and the spigot 15.

When the spigot 15 is inserted into the socket 13, the narrow part 32smaller in thickness than the first and second bulbs 28 and 29 iselastically deformed, so that the second bulb 29 can be easily expandedin the pipe diameter direction. Thus, only a small force is sufficientto expand the second bulb 29 in the pipe diameter direction. As aresult, the spigot 15 can be inserted into the socket 13 with a smallinsertion force (joining force).

As shown in FIG. 5, first, the distal end of the spigot 15 expands thesecond bulb 29 in the pipe diameter direction. After that, as shown inFIG. 6, the projection 24 compresses the first bulb 28. Thus, theexpansion of the second bulb 29 in the pipe diameter direction does notcoincide with the compression of the first bulb 28, so that the spigot15 can be inserted into the socket 13 with a small insertion force(joining force). Further, since the inner diameter J of the heel part 26is larger than the inner diameter K of the first bulb 28 as shown inFIG. 3, when the first bulb 28 is compressed, a part of the first bulb28 can escape into a gap between the heel part 26 and the spigot 15.Also with this configuration, the spigot 15 can be inserted into thesocket 13 with a small insertion force.

As shown in FIG. 6, when the first bulb 28 is interposed and compressedbetween the outer peripheral surface of the projection 24 and the innercircumferential surface of the projection 20, the recesses 31, 33, and34 specifically shown in FIG. 2 serve as a relief margin, so that theamount of the compressed second bulb 29 is reduced. Thus, the projection24 of the spigot 15 can smoothly pass by the inner circumference of thefirst bulb 28, so that the spigot 15 can be inserted into the socket 13with a small insertion force (joining force). As shown in FIG. 3, sincethe thickness t1 of the first bulb 28 is smaller than the thickness t2of the second bulb 29, the amount of the compressed first bulb 28 in thepipe diameter direction can be reduced, and the projection 24 of thespigot 15 can smoothly pass by the inner circumference of the first bulb28, thereby enabling the spigot 15 to be inserted into the socket 13with a small insertion force (joining force).

As shown in FIG. 7, when the projection 24 of the spigot 15 passesinside the annular second bulb 29, the gap 38 of FIG. 6 serves as arelief margin, and the second bulb 29 is elastically displaced (diameterexpansion) outward in the pipe diameter direction to escape from theprojection 24. Thus, the spigot 15 can be inserted into the socket 13with an even smaller insertion force (joining force).

If hydraulic pressure is applied in the pipes 12 and 14 joined to eachother, as shown in FIG. 1, push-out force F1 is applied by the hydraulicpressure to push out the bulb part 27 from the inner side towards theopening side of the socket 13. On the other hand, the first sealingportion 35 is not aligned with the second sealing portion 36 in the pipeaxial direction, so that the bulb part 27 can be prevented from beingpushed out from the inner side to the opening side of the socket 13 bythe push-out force F1. In particular, as the amount of misalignment (A)between the first sealing portion 35 and the second sealing portion 36in the pipe axial direction in FIG. 1 increases, the bulb part 27 can beprevented from being pushed out by larger push-out force F1. Thus, thesealing properties between the socket 13 and the spigot 15 are improved.

Since the diameter of traverse section of the second bulb 29 (=2×r2) islarger than the space S in the pipe diameter direction between the innercircumferential surface of the projection 20 of the socket 13 and theouter peripheral surface of the spigot 15, even if the bulb part 27 ispushed out by the push-out force F1, the second bulb 29 hardly passesthrough the space S. Thus, the bulb part 27 can be prevented from beingpushed out from the inner side to the opening side of the socket 13.

Moreover, hydraulic pressure is applied also to the gap 37, push-outforce F2 is applied towards the pipe center onto the second bulb 29.Thus, the second sealing portion 36 of the second bulb 29 is pressedhard against the outer peripheral surface of the spigot 15, so that thesealing properties are further improved between the socket 13 and thespigot 15.

In the configuration of FIG. 1, when the other pipe 12 and the one pipe14 are joined to each other with the spigot 15 inserted into the socket13, the inner circumferential surface of the first bulb 28 contacts theouter peripheral surface of the spigot 15. Instead of thisconfiguration, a gap may be formed between the inner circumferentialsurface of the first bulb 28 and the outer peripheral surface of thespigot 15. In this case, when the bulb part 27 is pushed out by thepush-out force F1, the second bulb 29 is pushed so as to enter the gapbetween the inner circumferential surface of the first bulb 28 and theouter peripheral surface of the spigot 15, so that an improvement insealing properties between the socket 13 and the spigot 15 can beexpected.

In a known technique, a straight pipe having a prescribed length is cutbased on an actually measured pipe dimension at a construction site toadjust the pipe length, so that the cut pipe may be connected to anotherpipe. Referring to FIGS. 8 to 15, the following will describe an examplein which the pipe joint shown in FIGS. 1 to 7 is applied when the cutpipe is connected to the other pipe.

In FIG. 8, reference numeral 41 denotes a pipe joint in which a cut pipe42 is connected to another pipe 43 via a connecting pipe 44. The cutpipe 42 is obtained by cutting a pipe at a conduit construction site tohave a prescribed length. The cut end of the pipe 42 constitutes aspigot 46. The other pipe 43 is a standard straight pipe having a spigot(not shown) at one end and a socket 13 at the other end.

The connecting pipe 44 is made of ductile cast iron, and has a socket 47at one end and a spigot 48 at the other end. The spigot 46 of the cutpipe 42 is inserted into the socket 47 of the connecting pipe 44, and aspigot 48 of the connecting pipe 44 is inserted into the socket 13 ofthe other pipe 43. Onto the cut end of the spigot 46 of the cut pipe 42,an annular anticorrosive material 49 which is made of, for example,rubber with water-tightness is attached.

The socket 47 of the connecting pipe 44 includes a detachment preventivemechanism 50 for preventing the socket 47 and the spigot 46 of the cutpipe 42 from being detached from each other and a sealing material 25.The socket 13 of the other pipe 43 includes a similar sealing material25 and a lock ring 22.

As shown in FIGS. 9 and 10, the detachment preventive mechanism 50 has aplurality of retaining members 51 disposed in the circumferentialdirection of the socket 47 and a wedging mechanism 53. The retainingmembers 51 can cut into the outer peripheral surface of the spigot 46 ofthe cut pipe 42 and move in the pipe diameter direction, and the wedgingmechanism 53 causes the retaining members 51 to cut in and move towardsan inward 52 side in the pipe diameter direction when the spigot 46 andthe socket 47 are relatively moving in a detachment direction.

A plurality of retaining recesses 54 are formed at intervals in thecircumferential direction on the inner circumferential surface of thesocket 47 of the connecting pipe 44. The retaining recesses 54 opentowards the inward 52 in the pipe diameter direction. The retainingmembers 51 are fitted in the retaining recesses 54 so as to cut in andmove towards the inward 52 in the pipe diameter direction. Edgecutting-in projections 55 are formed on the inner surfaces of theretaining members 51.

The wedging mechanism 53 has a receiving surface 57 formed on the outersurface of the retaining member 51 and a press bolt 58 for pressing theretaining member 51 towards the inward 52 in the pipe diameter directionvia the receiving surface 57. The receiving surface 57 is inclinedoutward in the pipe diameter direction as the receiving surface 57 iscloser to the inner side of the socket 47. The press bolt 58 is screwedwith a screw hole 59 penetrating the inner and outer sides of the socket47, and is inclined in an orthogonal direction to the receiving surface57 with a distal end in contact with the receiving surface 57.

The configuration of the socket 47 of the connecting pipe 44 forattaching the sealing material 25 is the same as that in the pipe jointof FIGS. 1 to 7.

The joint structure of the cut pipe 42 and the other pipe 43 includingthe configuration of the sealing material 25 is the same as that in thepipe joint of FIGS. 1 to 7.

In order to connect the cut pipe 42 to the other pipe 43 via theconnecting pipe 44, as shown in FIG. 11, the sealing material 25 isattached inside the socket 47 of the connection pipe 44.

After that, the spigot 46 of the cut pipe 42 is inserted into the socket47. At this point, as shown in FIG. 12, the distal end of the spigot 46is inserted to the inward side of a first bulb 28 and is brought intocontact with a second bulb 29 to push the second bulb 29 in theinsertion direction. Thus, as shown in FIG. 13, the second bulb 29 iselastically expanded (diameter expansion) in the pipe diameterdirection, so that a gap is formed across the periphery between theouter periphery of the expanded second bulb 29 and the bottom surface ofa recess 18. Then, as shown in FIG. 14, the spigot 46 is furtherinserted into the socket 47, so that the cut pipe 42 and the connectingpipe 44 are connected to each other.

Subsequently, as shown in FIG. 9, the press bolts 58 are tightened upand the retaining members 51 are pressed towards the inward 52 in thepipe diameter direction, so that the cutting-in projections 55 of theretaining members 51 cut into the outer peripheral surface of the spigot46.

The process of joining the spigot 48 of the connecting pipe 44 to thesocket 13 of the other pipe 43 is the same as that in the pipe joint ofFIGS. 1 to 7.

A conduit including a pipe joint having such a configuration is buriedin the ground in many cases. When earthquake deformation causes adetachment force (removal force) to be applied to the pipe joint 41, andthe connecting pipe 44 and the other pipe 43 are being detached andmoved relatively from each other, a projection 24 of the spigot 48 isengaged with the lock ring 22 from the socket inner side, so that thespigot 48 and the socket 13 are largely prevented from being detachedand moved from each other.

Further, when the detachment force is applied to relatively detach andmove the cut pipe 42 and the connecting pipe 44 from each other, thewedging mechanism 53 moves the retaining members 51 towards the inward52 side in the pipe diameter direction. Thus, the cutting-in projections55 cut into the outer peripheral surface of the spigot 46 of the cutpipe 42, so that the connection between the spigot 46 and the socket 47is forcibly maintained.

The cut end surface of the spigot 46 of the cut pipe 42 is not coatedbut the anticorrosive material 49 is attached to the cut pipe 42. Thus,the cut end surface can be prevented from being corroded.

The detachment preventive structure of the other pipe 43 and theconnecting pipe 44 and the detachment preventive structure of theconnecting pipe 44 and the cut pipe 42 may be any structure in additionto the above-described structure.

FIG. 15 is a modification example of the pipe joint shown in FIGS. 8 to14.

In FIG. 15, a detachment preventive mechanism 60 is provided on anannular detachment preventive ring 61 which is externally fitted acrossa spigot 46 of a cut pipe 42 and a portion beyond a socket 47 of aconnecting pipe 44. Similarly to the pipe joint of FIGS. 8 to 14, thedetachment preventive mechanism 60 has a plurality of retaining members51 and wedging mechanisms 53. A plurality of retaining recesses 54 areformed in the inner circumference of one end of the detachmentpreventive ring 61 in the pipe axial direction.

On the other end of the detachment preventive ring 61 in the pipe axialdirection, a fixing mechanism 62 for fixing the detachment preventivering 61 on the outer periphery of the socket 47 of the connecting pipe44 is provided. The fixing mechanism 62 has a groove 63 formed over theinner circumference of the detachment preventive ring 61, a fixed ring64 fitted into the groove 63, and a plurality of fixing bolts 65 forpressing the fixed ring 64 towards inward 52 in the pipe diameterdirection.

The fixed ring 64 is a metal ring singularly divided in thecircumferential direction, and is fitted onto the socket 47 of theconnecting pipe 44. The fixing bolts 65 are provided at intervals in thecircumferential direction of the fixed ring 64.

In such a configuration, during piping construction, the detachmentpreventive ring 61 is fitted onto the connecting pipe 44 from theopening side of the socket 47 with the fixed ring 64 fitted into thegroove 63, and the fixing bolts 65 are tightened up to press the fixedring 64 towards the inward 52 in the pipe diameter direction. Thus, thefixed ring 64 is pressed against the outer peripheral surface of theneck of the socket 47 while being engaged with the neck of the socket 47of the connecting pipe 44, so that the detachment preventive ring 61 isfixed on the outer periphery of the connecting pipe 44.

Next, the retaining members 51 are fitted into the retaining recesses54. In this state, the spigot 46 of the cut pipe 42 is inserted into thesocket 47 of the connecting pipe 44, and then a press bolt 58 istightened up to press the retaining member 51 towards the inward 52 inthe pipe diameter direction. Thus, cutting-in projections 55 cut intothe outer peripheral surface of the spigot 46 of the cut pipe 42.

With this configuration, when earthquake deformation causes a detachmentforce to be applied to the pipe joint, and the cut pipe 42 and theconnecting pipe 44 are relatively detached and moved from each other,the wedging mechanisms 53 cause the retaining members 51 to cut in andmove towards the inward 52 side in the pipe diameter direction, and thecutting-in projections 55 cut into the outer peripheral surface of thespigot 46. Thus, the connected state of the spigot 46 of the cut pipe 42and the socket 47 of the connecting pipe 44 is forcibly maintained.

FIGS. 16 and 17 show the cross-sectional structure of a pipe joint of amechanical type according to the present invention.

In the pipe joint, a socket 72 is formed on an end of one pipe 71 madeof ductile cast iron, and a spigot 74 inserted into the socket 72 isformed on an end of another pipe 73 made of ductile cast iron, the pipes71 and 73 being joined to each other. On the inner circumference of thesocket 72, a sealing material accommodating portion 75 is formed at theopening end of the socket 72 and a lock ring accommodating groove 76 isformed closer to the socket inner side than the sealing materialaccommodating portion 75. The sealing material accommodating portion 75has a tapered surface 75 a reduced in diameter from the opening endtowards the inner side of the socket 72, and a cylindrical surface 75 bextended with a constant diameter from the inner end of the taperedsurface 75 a towards the inner side of the socket 72.

In a space where the sealing material accommodating part 75 is provided,that is, a space between the inner circumferential surface of the socket72 and the outer peripheral surface of the spigot 74 where the sealingmaterial accommodating part 75 is formed, an annular sealing material 77made of rubber is accommodated. The sealing material 77 is pushed intothe inner side of the socket 72 by an annular-plate-like push ring 78made of metal. The push ring 78 is disposed on the outer periphery of aportion of the spigot 74 not inserted into the socket 72. Thus, thesealing material 77 is compressed between the inner circumferentialsurface of the socket 72 and the outer peripheral surface of the spigot74 to seal the space between the inner circumferential surface of thesocket 72 and the outer peripheral surface of the spigot 74.

The sealing material 77 integrally includes a circular distal endportion 77 a formed at a point serving as the distal end of the sealingmaterial 77 pushed into the socket 72, and a base portion 77 b having atrapezoidal cross section. The circular distal end portion 77 a has acircular cross section, and the trapezoidal cross section of the baseportion 77 b is thin at a point connected to the circular distal endportion 77 a and is thicker as it is closer to the push ring 78.

In the push ring 78, a stepped concave 79 is formed, into which a partof the base portion 77 b of the sealing material 77 is fitted, forpreventing the part of the base portion 77 b from moving in a diameterexpansion direction (outward in the pipe diameter direction).Specifically, a portion inward in the pipe diameter direction on asurface of the plate-like push ring 78 facing the socket 72 is morerecessed than a portion outward in the pipe diameter direction on thesurface, so as to be thinner in the pipe axial direction. The steppedconcave 79 has a concave bottom surface 79 a and a stepped portion 79 bformed at the boundary between the bottom surface 79 a and the portionoutward in the pipe diameter direction. The push ring 78 is attachedsuch that the end of the base portion 77 b of the sealing material 77 isfitted into the stepped concave 79 of the push ring 78.

As shown in FIG. 16, in a state in which the sealing material 77 isattached, a surface of the push ring 78 facing a flange 80 is closelyattached to the end surface of the flange 80 formed on the outerperiphery of the socket 72.

Specifically, as shown in FIG. 18, through holes 80 a extending in thepipe axial direction are formed in the flange 80. As shown in FIG. 19,through holes 78 a extending in the pipe axial direction are formed alsoin the push ring 78. As shown in FIGS. 16 and 17, bolts 81 for fasteningthe push ring 78 to the flange 80 pass through the through holes 80 aand 78 a.

As many through holes 78 a of the push ring 78 as the bolts 81 areequally spaced along the circumferential direction. Meanwhile, thethrough holes 80 a of the flange 80 equally spaced along thecircumferential direction are, for example, multiple times as many asthe bolts 81.

In the illustration, two fastening bolts 81 are used. Correspondingly,in the push ring 78, two through holes 78 a are formed at 180° intervalsalong the circumferential direction. In the flange 80, four throughholes 80 a are formed at 90° intervals along the circumferentialdirection.

In the lock ring accommodating groove 76, an annular lock ring 82singularly divided in the circumferential direction is accommodated.When the lock ring 82 is accommodated, the lock ring 82 is elasticallypressed against the outer periphery of the spigot 74. A projection 83 isformed on the outer periphery of the distal end portion of the spigot 74so as to be engaged with the lock ring 82.

In the above configuration, when the pipes 71 and 73 are joined to eachother, the lock ring 82 has been accommodated in the accommodatinggroove 76 of the socket 72, and the push ring 78 and the sealingmaterial 77 have been fitted onto the spigot 74. The spigot 74 in thisstate is inserted into the socket 72. Thus the projection 83 of thespigot 74 elastically pushes out the lock ring 82 and passes through thelock ring 82 to the inner side of the socket 72. After the projection 83passes through the lock ring 82, the lock ring 82 is pressed against theouter peripheral surface of the spigot 74 by the elastic force.

Thereafter, the sealing material 77 and the push ring 78 having beenfitted onto the spigot 74 are disposed at positions shown in FIG. 17.Specifically, the distal end portion of the sealing material 77 comesinto contact with the tapered surface 75 a of the accommodating portion75, and the sealing material 77 and the push ring 78 are disposed atsuch a position that the push ring 78 is in contact with the baseportion 77 b of the sealing material 77. Further, the bolts 81 are madeto pass through the through holes 78 a of the push ring 78 and thethrough holes 80 a of the flange 80 to screw the bolts 81 into nuts 84.

At this point, since the stepped concave 79 is formed in the push ring78, the base portion 77 b of the sealing material 77 is fitted into thestepped concave 79 of the push ring 78 only by bringing the sealingmaterial 77 into contact with the push ring 78. The centers of thesealing material 77 and push ring 78 are aligned with each other. Thusthe centering of the sealing material 77 can be easily performed.

After that, the bolts 81 are tightly screwed into the nuts 84, therebymoving the push ring 78 towards the flange 80 to compress and insert thesealing material 77 into the accommodating portion 75. Specifically,first, as shown in FIG. 17, the circular distal end portion 77 a of thesealing material 77 comes into contact with the tapered surface 75 a ofthe sealing material accommodating portion 75, and the sealing material77 is entirely accommodated in the accommodating portion 75 while beingguided by the tapered surface 75 a.

At this point, in response to the force of the push ring 78 pushing thesealing material 77, a reaction force is generated to push back thesealing material 77 to the push ring 78 side, from the tapered surface75 a of the sealing material accommodating portion 75 in contact withthe circular distal end portion 77 a of the sealing material 77 and theouter peripheral surface of the spigot 74. The reaction force moves thebase portion 7 b of the sealing material 77 along the pressing surfaceof the pressing ring 78 in the diameter expansion direction, with acontact portion of the outer peripheral surface of the spigot 74 and theinner circumferential surface of the socket 72 at the circular distalend portion 77 a of the sealing material 77 as the fulcrum of moment.

However, since the stepped concave 79 is formed in the push ring 78 toprevent the base portion 77 b of the sealing material 77 from moving inthe diameter expansion direction, that is, outward in the pipe diameterdirection, the sealing material 77 is prevented from being moved in thediameter expansion direction. As a result, the base portion 77 b of thesealing material 77 does not move in the diameter expansion direction.Thus the sealing material 77 is satisfactorily accommodated in theaccommodating portion 75 and is placed in a favorable compressed state.After that, until the push ring 78 is sufficiently brought into contactwith the flange 80, that is, the push ring 78 and the flange 80 are in ametal touch state, the nuts 84 are tightened up.

In this configuration, since the sealing material 77 is pressed with thepush ring 78 sufficiently brought into contact with the flange 80 formedon the outer periphery of the socket 72, the sealing material 77 issatisfactorily compressed between the socket 72 and the spigot 74 onlyby closely attaching the push ring 78 to the flange 80. This eliminatesthe need for carefully controlling intervals between the push ring andthe flange, unlike in a known mechanical pipe joint. Thus, the push ring78 can be efficiently attached to the flange 80 and the sealing material77 can be easily held in a favorable compressed state.

Further, the push ring 78 is provided only to push the sealing material77 into the accommodating portion 75 and hold the pushed sealingmaterial 77 in the accommodating portion 75 against a fluid pressure inthe socket 72. Compared to the known mechanical pipe joint in which abolt causes a compression force to act on a sealing material to exhibitdesired sealing properties, the present embodiment can reduce thetightening force and the number of bolts 81.

Moreover, the push ring 78 has the stepped concave 79, so that thesealing material 77 can be satisfactorily held in the accommodatingportion 75 without moving in the diameter expansion direction when thepush ring 78 presses the sealing material 77. Thus, even if the circulardistal end portion 77 a of the sealing material 77 has a larger crosssection than that in the known pipe joint, the sealing material 77 canbe inserted into the accommodating portion 75 without any difficulties.With this configuration, after the sealing material 77 is onceaccommodated in the accommodating portion 75, the circular distal endportion 77 a of the compressed sealing material 77 receives a relativelylarge force to adhere tightly to the cylindrical surface 75 b of thesealing material accommodating portion 75 and the outer peripheralsurface of the spigot 74. In other words, after the push ring 78 ismoved until the push ring 78 comes into close contact with the flange80, it is not necessary to constantly apply a high specific pressure tothe sealing material 77 by the push ring 78. Thus, even in the casewhere the nuts 84 are loosened, the sealing properties of the sealingmaterial 77 can be favorably maintained.

In the illustration, in the flange 80 formed on the outer periphery ofthe socket 72, the through holes 80 a twice as many as the bolts 81actually used are formed. Thus, even in the case where the pipe 71having the socket 72 is a deformed pipe buried in a predeterminedorientation in the ground, the bolts 81 may be inserted into the throughholes 80 a of the socket 72 not positioned at the bottom of the pipe 71.

Specifically, when only two through holes 80 a of the flange 80 of thesocket 72 as many as the bolts 81 are formed, the through holes 80 a maybe forced to be arranged at the upper portion (pipe top) and the lowerportion (pipe bottom) of the flange 80. In such a case, the bolts 81have to pass through the through holes 80 a and 78 a at the pipe bottomserving as the ground contact area, and the nuts 84 have to be tightenedup, thereby disadvantageously involving much time and effort. On theother hand, in the illustration, even in similar conditions, the throughhole 80 a in the side portion of the flange 80 may be selected to havethe bolt 81 placed into the through hole 80 a. Specifically, the bolts81 can be placed away from the bottom of the pipe 71 and the bolts 81can be efficiently tightened up.

The number of bolts 81 is not limited to two as in the illustration, butthe same configuration may be adopted even when the number of bolts 81is at least three. In such a case, the number of through holes 78 aformed in the push ring 78 corresponds to the number of bolts 81, andthrough holes 80 a twice (or an integer at least three times ispossible) as many as the through holes 78 a may be formed in the flange80.

Since the push ring 78 can freely rotate about the axis, the throughholes 78 a as many as the bolts 81 have only to be formed.

In contrast, the through holes 80 a as many as the bolts 81 (the throughholes 78 a of the push ring 78) may be formed in the flange 80. Inaddition, a sealing material having a circular distal end portion 77 awhich is not as large as that in the illustration may be used as in theknown pipe joint. Thus, in the pipe joint having the known structure,only a push ring 78 is changed to the plate-like push ring having thestepped concave 79 as in the illustration, so that existing products maybe used for parts other than the push ring 78.

As shown in FIGS. 16 and 17, the stepped concave 79 is formed only onthe surface of the push ring 78 facing the socket 72. However, inaddition to this, as shown in FIG. 20, a stepped concave 79 may beformed also on a surface opposed to the surface of the push ring 78facing the socket 72. Specifically, stepped concaves 79 may be providedon two surfaces of the plate-like push ring 78.

In the configuration in which the stepped concaves 79 are provided onthe two surfaces of the plate-like push ring 78, when the push ring 78is fitted onto a spigot 74 beforehand, a sealing material 77 is reliablyfitted into the stepped concave 79 in joining the pipes, no matter whichone of the two surfaces of the push ring 78 the socket 72 faces.Regardless of the orientation of the surface of the push ring 78, nuts84 can be tightened up until the push ring 78 is reliably brought intoclose contact with a flange 80.

Therefore, since the stepped concaves 79 are formed on the two surfacesof the push ring 78, when the push ring 78 is fitted onto the spigot 74,an operator does not have to worry about misorienting the surfaces ofthe push ring. Thus, operation errors can be avoided and theconfirmation of orientation of the surfaces can be omitted, so that theoperation efficiency can be improved.

FIGS. 21 to 24 show a modification example of the pipe joint accordingto the present invention.

As shown in FIGS. 21 and 22, a push ring 78 has a center hole portion 86formed so as to penetrate the push ring, a plurality of through holes 78a formed in the circumferential direction for allowing bolts 81 to passthrough the through holes 78 a, and joint surfaces 87 in contact withthe opening end surface of a socket 72. The inner diameter of the centerhole portion 86 of the push ring 78 is set larger by a predetermineddimension than the outer diameter of a spigot 74.

On two surfaces of the push ring 78 along the pipe axial direction,annular stepped concaves 79 are formed. The end of a base portion 77 bof a sealing material 77 is fitted into the stepped concave 79. Theconcave 79 has a bottom surface 79 a and a constraint surface 79 cformed in the vicinity of the bottom surface 79 a.

Reference numeral 88 denotes a centering mechanism. The centeringmechanism 88 has the constraint surface 79 c of the stepped concave 79of the push ring 78 and a tapered surface 77 c formed over the outerperipheral edge of the base portion 77 b of the sealing material 77.

The constraint surface 79 c of the concave 79 is tapered such that thediameter of the constraint surface is gradually expanded towards thesocket 72. The tapered surface 77 c of the sealing material 77 is formedalong the tapered portion of the constraint surface 79 c. Specifically,the tapered surface 77 c of the sealing material 77 is formed such thatthe diameter of the tapered surface 77 c is gradually expanded towards acircular distal end portion.

Inclination angle α of the constraint surface 79 c and inclination angle13 of the tapered surface 77 c with respect to the pipe diameterdirection are the same and, for example, 60°. The concave bottom surface79 a of the push ring 78 and the end surface of the base portion 77 b ofthe sealing material 77 are formed in the pipe diameter direction.

In such a configuration, when one pipe 71 and another pipe 73 are joinedto each other, as shown in FIG. 23, first, a lock ring 82 is fitted intoa lock ring accommodating groove 76 in the socket 72. Further, as in theillustration, the sealing material 77 and the push ring 78 are fittedonto the spigot 74, and the distal end portion of the base portion 77 bof the sealing material 77 is fitted into the concave 79 of the pushring 78. In this state, the spigot 74 is inserted into the socket 72.

When a projection 83 of the spigot 74 passes through the innercircumference of the lock ring 82 towards the inner side of the socket72, the bolts 81 are inserted through the through holes 80 a and thethrough holes 78 a. As shown in FIG. 24, nuts 84 are tightened up tomove the push ring 78 closer to the socket 72. Thus, as shown in FIG.21, the sealing material 77 is pushed by the push ring 78 into a gapbetween the outer peripheral surface of the spigot 74 and the innercircumferential surface of the socket 72, and is accommodated in asealing material accommodating portion 75. The nuts 84 are tightened upto bring the joint surface 87 of the plate-like push ring 78 intocontact with the end surface of the socket 72.

At this point, the end of the base portion 77 b of the sealing material77 is constrained in the pipe diameter direction by the constraintsurface 79 c of the concave 79. Thus, the end of the base portion 77 bof the sealing material 77 is prevented from moving (deforming) alongthe bottom surface 79 a of the concave 79 in the pipe diameterdirection, so that the base portion 77 b of the sealing material 77 isnot interposed between the joint surface 87 of the push ring 78 and theopening end surface of the socket 72 (effect of preventing the sealingmaterial 77 from being interposed). In addition, the joint surface 87 ofthe push ring 78 is brought into surface contact with the opening endsurface of the socket 72, so that the sealing material 77 can besatisfactorily inserted into the accommodating portion 75.

In the above-described joining step, as shown in FIG. 23, when thesealing material 77 and the push ring 78 are fitted onto the spigot 74,the center of the push ring 78 is placed below the pipe axis by theaction of gravity. Thus, a gap 89 between the inner circumference of thecenter hole portion 86 of the push ring 78 and the outer periphery ofthe spigot 74 is the smallest (=0) at the pipe top and the largest atthe pipe bottom.

In this state, when the nuts 84 are tightened up to move the push ring78 in the pipe axial direction, as shown in FIG. 24, the constraintsurface 79 c of the push ring 78 is guided in contact with the taperedsurface 77 c of the sealing material 77 along the pipe diameterdirection. Thus, the push ring 78 gradually rises against the spigot 74,so that the center of the push ring 78 is aligned with the pipe axis.That is, the push ring 78 is automatically centered (effect ofautomatically centering the push ring 78). While the centered state ismaintained, as shown in FIG. 21, the one pipe 71 and the other pipe 73are joined to each other. This saves an operator the effort of liftingup and moving the push ring 78 in the pipe diameter direction andcentering the push ring 78.

As in the illustration, since the stepped concaves 79 are formed on thetwo surfaces of the push ring 78, when the pipes 71 and 73 are joined toeach other, the push ring 78 may be fitted onto the spigot 74 in anydirection.

FIG. 25 shows a modification example of the pipe joint shown in FIGS. 21to 24. In the pipe joint shown in FIGS. 21 to 24, as specifically shownin FIG. 22, the centering mechanism 88 has the tapered constraintsurface 79 c formed in the stepped concave 79 of the push ring 78 andthe tapered surface 77 c formed at the end of the base portion 77 b ofthe sealing material 77. Instead, in the modification example of FIG.25, a sealing material 77 does not have a tapered surface, and acentering mechanism 88 has only a tapered constraint surface 79 c.

In this configuration, the nuts 84 are tightened up to move the pushring 78 in a push direction, so that the constraint surface 79 c of thepush ring 78 is brought into contact with the outer peripheral edge of abase portion 77 b of the sealing material 77 and guided in the pipediameter direction.

FIGS. 26 to 28 show another modification example of the pipe joint shownin FIGS. 21 to 24. In the modification example, a constraint surface 79c has a straight portion 91 formed in a direction orthogonal to a bottomsurface 79 a, and a tapered portion 92 diameter-expanded towards thesocket 72. The straight portion 91 is positioned on the bottom side of aconcave 79, and the tapered portion 92 is positioned on the opening sideof the concave 79. As shown in FIG. 28, the straight portion 91 isfitted into the end of the base portion 77 b of the sealing material 77having no tapered surface at the outer peripheral edge of the end of thebase portion 77 b.

In such a configuration, as shown in FIG. 26, when the nuts 84 aretightened up to move a push ring 78 closer to the socket 72, the taperedportion 92 of the constraint surface 79 c of the push ring 78 is broughtinto contact with the peripheral edge of the end of the base portion 77b of the sealing material 77 and is guided in the pipe diameterdirection. Thus, as shown in FIG. 27, the push ring 78 gradually risesagainst the spigot 74, the center of the push ring 78 is aligned withthe pipe axis, and the push ring 78 is automatically centered. Further,as shown in FIG. 28, the end of the base portion 77 b of the sealingmaterial 77 is fitted into the straight portion 91 of the constraintsurface 79 c, and in this state, the one pipe 71 and the other pipe 73are joined to each other.

As shown in FIG. 28, the end of the base portion 77 b of the sealingmaterial 77 is fitted into the straight portion 91 of the constraintsurface 79 c, so that the base portion 77 b of the sealing material 77is reliably constrained by the straight portion 91 of the constraintsurface 79 c in the diameter expansion direction. Thus, the base portion77 b of the sealing material 77 can be prevented from moving (deforming)along the bottom surface 79 a of the concave 79 in the pipe diameterdirection.

FIG. 29 shows still another modification example of the pipe joint shownin FIGS. 21 to 24. In this modification example, constraint surfaces 79c of a push ring 78 are not tapered but straight in the pipe axialdirection. Thus, a centering mechanism 88 includes only a taperedsurface 77 c of a sealing material 77.

In this configuration, the nuts 84 are tightened up to move the pushring 78 closer to the socket 72, so that the corner portion of theconstraint surface 79 c and a joint surface 87 of the push ring 78 isbrought into contact with the tapered surface 77 c of the sealingmaterial 77. Thus, the push ring 78 is guided in the pipe diameterdirection.

The following will describe the inclination angle α of the constraintsurface 79 c and the inclination angle 13 of the tapered surface 77 c ofthe sealing material 77 which are shown in FIG. 22. It is preferablethat the inclination angles α and β are set to be 60° as describedabove, but the inclination angles may be set in a range of 50° to 80°.

Table 1 shows experimental results obtained by determining whether theabove-described “effect of preventing the sealing material 77 from beinginterposed” is produced and whether the above-described “effect ofautomatically centering the push ring 78” is produced when theinclinations angles α and β are changed. As described above, the effectof preventing the sealing material 77 from being interposed” is aneffect of preventing the end of the base portion 77 b of the sealingmaterial 77 from being interposed between the joint surface 87 of thepush ring 78 and the opening end surface of the socket 72. Further, theeffect of automatically centering the push ring 78″ is an effect ofautomatically centering the push ring 78 with respect to the spigot 74.

As shown in Table 1, the inclination angles α and β are set in a rangeof 50° to 80°, so that both the effect of preventing the sealingmaterial 77 from being interposed and the effect of automaticallycentering the push ring 78 are surely exerted.

In contrast, in the case where the inclination angles α and β are setless than 50°, the constraint function of the constraint surface 79 c isinsufficient for the base portion 77 b of the sealing material 77, sothat the base portion 77 b of the sealing material 77 easily slidesalong the constraint surface 79 c and moves (deforms) in the diameterexpansion direction. Conversely, in the case where the inclinationangles α and β exceed 80°, the push ring 78 insufficiently rises againstthe spigot 74, the center of the push ring 78 is not aligned with thepipe axis.

The inclination angle α of the constraint surface 79 c of the push ring78 and the inclination angle β of the tapered surface 77 c of thesealing material 77 may be the same or different from each other withina range of 50° to 80°.

TABLE 1 Inclination Effect of preventing sealing Effect of automaticallyangle (°) material from being interposed centering push ring 30 Notproduced Produced 35 Not produced Produced 40 Not produced Produced 45Not produced Produced 50 Produced Produced 55 Produced Produced 60Produced Produced 65 Produced Produced 70 Produced Produced 75 ProducedProduced 80 Produced Produced 85 Produced Not produced 90 Produced Notproduced

In the embodiment of FIGS. 21 to 29, the stepped concaves 79 are formedon the two surfaces of the plate-like push ring 78. However, the concave79 may be formed on only one of the two surfaces of the plate-like pushring 78.

FIGS. 30 to 33 show another embodiment of the present invention.

In the illustration, a stepped concave 79 and a sealing material 77 donot have a tapered surface. However, the stepped concave 79 and thesealing material 77 may have a tapered surface.

A plurality of spacers 95 are interposed between a side surface 93 of apush ring 78 and an end surface 94 of a socket 72. As shown in FIGS. 30and 31, the spacers 95 are integrally formed on two surfaces of theplate-like push ring 78 made of ductile cast-iron. In the illustration,two spacers 95 are disposed at 180° intervals along the circumferentialdirection of the push ring 78. Two through holes 78 a of the push ring78 are disposed at 180° intervals along the circumferential direction ofthe push ring 78. The spacers 95 and the through holes 78 a are formedin the same positions along the circumferential direction of the pushring 78. The spacers 95 are formed closer to the outer side along thediameter direction of the push ring 78 than the through holes 78 a. Thespacers 95 are formed in a truncated conical shape so as to project fromthe push ring 78 in the pipe axial direction as in the illustration.Height M from the side surface 93 of the push ring 78 to the distal endportion of the spacer 95 is set constant.

In this configuration, when one pipe 71 and another pipe 73 are joinedto each other, as shown in FIG. 32, after a spigot 74 is inserted intothe socket 72, bolts 81 are made to pass through the through holes 78 aof the push ring 78, and nuts 84 are tightened up to move the push ring78 closer to the socket 72. Thus, the sealing material 77 is pushed intoa gap between the outer peripheral surface of the spigot 74 and theinner circumferential surface of the socket 72 by the push ring 78 andis accommodated in an accommodating portion 75.

The push ring 78 is moved closer to the socket 72 in this way, so thatthe distal ends of the spacers 95 hit against the end surface 94 of thesocket 72. Thus, a gap 96 between the side surface 93 of the push ring78 and the end surface 94 of the socket 72 can be accurately and easilykept at a value equal to the height M of the spacer 95. As a result, thesealing material 77 can be prevented from being insufficient in sealingproperties and pushed by an excessive force.

Further, the state of the attached sealing material 77 can be visuallyconfirmed through the gap 96. As shown in FIG. 33, a specialthin-plate-like gauge 97 is inserted into the gap 96, and the distal endof the gauge 97 is brought into contact with the outer peripheralsurface of a base portion 77 b of the sealing material 77, so that adistance in the diameter direction from the outer peripheral surface ofa flange 80 of the socket 72 or the outer peripheral surface of the pushring 78 to the outer peripheral surface of the base portion 77 b of thesealing material 77 can be measured. Thus, the state of the attachedsealing material 77 can be confirmed more accurately.

As in the illustration, since the spacers 95 are arranged along with thethrough holes 78 a in the same diameter direction and the spacers 95 arepositioned near the through holes 78 a, as shown in FIG. 30, when thepush ring 78 is fastened to the flange 80 of the socket 72 by the bolts81 and the nuts 84, the tightening force of the bolts 81 acts in thevicinity of the spacers 95. Thus, the bending deflection of the pushring 78 in the thickness direction can be reduced.

As shown in FIG. 34, the spacers 95 may be formed closer to the innerside in the diameter direction of the push ring 78 than the throughholes 78 a.

As shown in FIGS. 35 and 36, the spacers 95 may be displaced from thethrough holes 78 a by a predetermined angle in the direction of the pushring 78. In the illustration, the predetermined angle is 90°.

In the above-described embodiment, the through holes 78 a and thespacers 95 are respectively formed at two points in the circumferentialdirection of the push ring 78, but the number of through holes 78 a andspacers 95 is not limited to two. The through holes 78 a and the spacers95 may be formed at more than two points. The spacers 95 may be formedon only one of the two surfaces of the plate-like push ring 78. Thenumber of through holes 78 a and the number of spacers 95 provided onone of the side surfaces 93 of the push ring 78 may be the same ordifferent from each other as described above.

The spacers 95 may be integrally formed not in the push ring 78 asdescribed above but in the socket 72 of the pipe 71 made of ductilecast-iron. Alternatively, the spacers 95 may be formed on both the sidesurface 93 of the push ring 78 and the end surface 94 of the socket 72.

As shown in FIGS. 37 and 38, the spacers 95 may be formed in a memberseparated from the push ring 78 and the socket 72. In the illustration,the spacers 95 are provided in an annular thin plate member 98. Thespacers 95 and the thin plate member 98 may be integrally resin-molded.In this configuration, the sum of the height of the spacer 95 and thethickness of the thin plate member 98 is a predetermined dimension M.

In this configuration, the thin plate member 98 and the spacers 95integrally formed are interposed and held between the side surface 93 ofthe push ring 78 and the end surface 94 of the socket 72. Thus, the gap96 between the side surface 93 of the push ring 78 and the end surface94 of the socket 72 can be accurately and easily kept at thepredetermined dimension M.

In the above-described embodiments, the spacers 95 are formed in atruncated conical shape but may be formed in any shape. For example, asshown in FIG. 39, the spacers 95 may be elliptical in thecircumferential direction of the push ring 78 or the socket 72.

Even in the embodiment in which the spacers 95 are used, the steppedconcaves 79 of the push ring 78 may be provided on the two surfaces orone of the two surfaces of the plate-like push ring 78.

FIGS. 40 to 44 show still another embodiment of the present invention.This embodiment is different from the above-described embodiments in theconfiguration of a sealing material 77. FIG. 41 is a cross-sectionalview showing an uncompressed sealing material 77. A base portion 77 b ofthe sealing material 77 has the same configuration as that in FIG. 22.In contrast, a circular distal end portion 77 a of the sealing material77 is different from that in FIG. 22.

An arc portion 101 is formed at the distal end of the circular distalend portion 77 a, and in continuity with the arc portion 101, acylindrical portion 104 is formed which has an outer peripheral surface102 and an inner circumferential surface 103 both formed in the pipeaxial direction. In continuity with the cylindrical portion 104, an arcportion 105 connected to the base portion 77 b is formed. On the outerperiphery of the base portion 77 b, a tapered surface 106 is formed, thediameter of which is gradually reduced towards the circular distal endportion 77 a. Reference numeral 107 denotes the end surface of the baseportion 77 b.

FIG. 42 is a cross-sectional view showing the process of accommodatingthe sealing material 77 in an accommodating portion 75. As shown in FIG.42, a push ring 78 is in contact with the end surface 107 of the baseportion 77 b and the end of the base portion 77 b is fitted into astepped concave 79, in a state in which the circular distal end portion77 a of the sealing material 77 is in contact with a tapered surface 75a of a socket 72. As shown in FIG. 43, the stepped concave 79 has atapered portion 92 at inclination angle α. In the example of FIGS. 40 to42, the sealing material 77 does not have a tapered surface, but asshown in FIG. 44, the sealing material may have a tapered surface 77 cat inclination angle β.

When the sealing material 77 is pushed into the accommodating portion 75further than the state of FIG. 42, the sealing material 77 is completelyaccommodated in the accommodating portion 75 as shown in FIG. 40. Thus,the tapered surface 106 of the sealing material 77 is brought intocontact with the tapered surface 75 a of the accommodating portion 75.When the tapered surfaces 106 and 75 a contact each other, a spacer 95of the push ring 78 is metal-touch-joined to an end surface 94 of thesocket 72. Thus, after the tapered surface 106 of the sealing material77 is brought into contact with the tapered surface 75 a of theaccommodating portion 75, the tapered surface 106 of the sealingmaterial 77 is further pressed against the tapered surface 75 a of theaccommodating portion 75 to prevent the sealing material 77 from beingdeformed.

A cylindrical surface 75 b of the accommodating portion 75 of the socket72 and the outer peripheral surface of a spigot 74 form a space 108. Thecylindrical surface 75 b and the outer peripheral surface of the spigot74 are arranged in a concentric manner. In the space 108, the circulardistal end portion 77 a of the sealing material 77 is accommodated, andthe cylindrical portion 104 is brought into contact with the cylindricalsurface 75 b and the outer peripheral surface of the spigot 74. Theouter peripheral surface 102 and the inner circumferential surface 103forming the cylindrical portion 104 are uniformly compressed whilekeeping the concentric state even after the circular distal end portion77 a is accommodated in the space 108.

The outer peripheral surface 102 and the inner circumferential surface103 are in surface-contact with the cylindrical surface 75 b and theouter peripheral surface of the spigot 74 over the periphery and areuniformly compressed, so that desired sealing properties are exhibited.The circular distal end portion 77 a does not exhibit sealing propertiesby receiving a reaction force against the force of the push ring 78pressing the sealing material 77.

The following will describe the case where the sealing material 77receives a fluid pressure in the pipe. The circular distal end portion77 a tends to expand in the pipe diameter direction by the fluidpressure, but the expansion is limited by the cylindrical surface 75 bof the socket 72 and the outer peripheral surface of the spigot 74.Thus, the circular distal end portion 77 a is additionally provided witha compression force by the fluid pressure. The outer peripheral surface102 and the inner circumferential surface 103 are in surface-contactwith the cylindrical surface 75 b of the socket 72 and the outerperipheral surface of the spigot 74 over the periphery while keeping theconcentric state even after the circular distal end portion 77 areceives the fluid pressure in the pipe, and are uniformly compressedwith the compression force added by the fluid pressure in the pipe.Thus, the sealing properties are sufficiently exhibited.

The following will describe the case where the circular distal endportion 77 a is compressed by the fluid pressure in the pipe to movetowards the opening side of the socket 72. If the circular distal endportion 77 a moves within the length of the cylindrical portion 104 inthe pipe axial direction, even after the circular distal end portion 77a moves, the surface-contact of the outer peripheral surface 102 and theinner circumferential surface 103 of the sealing material 77, thecylindrical surface 75 b of the socket 72, and the outer peripheralsurface of the spigot 74 over the periphery is kept within a certainarea along the pipe axial direction. Thus, the desired sealingproperties are maintained.

As described above, the sealing material 77 has the cylindrical portion104 in which the outer peripheral surface 102 is formed concentricallywith the cylindrical surface 75 b of the socket 72, and the innercircumferential surface 103 is formed concentrically with the outerperipheral surface of the spigot 74. Thus, when the sealing material 77is compressed between the socket 72 and the spigot 74, the cylindricalportion 104 is in surface-contact with the outer peripheral surface ofthe spigot 74 and the inner circumferential surface of the socket 72over the periphery. As a result, the sealing material 77 can beuniformly brought into surface-contact with the socket 72 and the spigotover a wide area to maintain the sealing properties. Further, even whena portion of the sealing material 77 exhibiting sealing properties undera fluid pressure in the pipe moves, the desired sealing properties aremaintained.

FIGS. 45 to 49 show a slip-on detachment preventive pipe joint accordingto another embodiment.

In the pipe joint, between the outer peripheral surface of a lock ring22 and the inner circumferential surface of an accommodating groove 19,a centering member 111 made of rein is disposed for holding andcentering the lock ring 22 before a spigot 15 is inserted into a socket13. A tapered surface 112 is formed at the distal end of a projection 24of the spigot 15 so as to be tapered towards the distal end side of thespigot 15. A tapered surface 113 is formed on the inner circumferentialpart of the lock ring 22 on the socket opening side, so as to expandtowards the socket opening side. When the spigot 15 is inserted into thesocket 13, the tapered surface 112 at the distal end of the projection24 of the spigot 15 and the tapered surface 113 of the lock ring 22 arein slidable contact with each other, thereby elastically expanding thediameter of the lock ring 22.

As in the illustration, on the inner circumferential surface of thesocket 13, three inner circumferential projections 114, 115, and 116 areformed in this order from the opening side towards the inner side of thesocket 13. The three inner circumferential projections 114, 115, and 116form an accommodating groove for accommodating a sealing material 25 andthe lock ring accommodating groove 19. The three inner circumferentialprojections 114, 115, and 116 are formed to have a larger inner diameterthan the outer diameter of the projection 24 such that the projection 24of the spigot 15 can be inserted into the socket 13. More specifically,the inner circumferential projections 114 and 116 at the opening partand inner part of the socket are larger in inner diameter than the innercircumferential projection 115 at the middle part. In other words, theinner diameter of the inner circumferential projection 115 at the middlepart is the smallest.

With this configuration, the spigot 15 can be swung about the innercircumferential projection 115 at the middle part such that the axis ofthe spigot 15 is bent and misaligned with the axis of the socket 13. Asa result, the flexibility of connected state of the socket 13 and thespigot 15 is increased. Further, when the spigot 15 is inserted into thesocket 13, the socket 13 and the spigot 15 can be satisfactorilyconnected to each other even in a state where the axes of the socket 13and the spigot 15 are not accurately aligned with each other, forexample, the axes are bent.

However, when the inner circumferential projection 116 on the socketinner side is larger in inner diameter than the inner circumferentialprojection 115 at the middle part, the lock ring 22 may not be preventedfrom projecting towards the socket inner side by being pushed by theprojection 24 when the spigot 15 is inserted.

In order to address the problem, as shown in FIGS. 45 to 48, a holder117 and a hold width 118 are integrally formed in the centering member111 so that the traverse section of the holder and the hold width isL-shaped. The holder 117 is disposed between the inner circumferentialsurface of the accommodating groove 19 and the outer peripheral surfaceof the lock ring 22 to hold the lock ring 22 from the outer peripheralside thereof. The hold width 118 protrudes inward in the pipe diameterdirection from the socket inner side part of the holder 117 and entersbetween the inner side surface of the accommodating groove 19 and theinner side surface of the lock ring 22, so that the hold width 118 iscaught by the inner side surface of the lock ring 22 when the spigot 15is inserted into the socket 13. Thus, the lock ring 22 is prevented fromprojecting from the accommodating groove 19 towards the inner side ofthe socket 13.

The hold width 118 and the holder 117 are plurally divided along thecircumferential direction, and curved-plate-like connecting parts 120are integrally formed on the outer peripheral surfaces of divided parts119. The connecting parts 120 are disposed in arc shape on the dividedparts 119 in an elastically deformable state and are brought intocontact with the inner circumferential surface of the accommodatinggroove 19. Further, the divided parts 119 are connected to each other soas to move in the pipe diameter direction while elastically pushing eachother inward in the pipe diameter direction.

The centering member 111 made of resin is formed of polypropylene ornylon 6. The overall centering member 111, that is, the holder 117, thehold width 118, and the connecting parts 120 are integrally formed.

In FIGS. 45 to 48, the connecting parts 120 and the holder 117 areformed with the same width but the present invention is not limited tothis. The connecting parts 120 may be different from the holder 117 inwidth.

As shown in FIG. 46 in an enlarged manner, the hold width 118 of thecentering member 111 is formed in such a dimension that an end 121 ofthe hold width 118 on the inner side in the diameter direction protrudesmore inward in the pipe diameter direction than the innercircumferential part of the inner circumferential protrusion 116 at thesocket inner side while the centering member 111 is centered in the lockring accommodating groove 19.

Since the connecting part 120 is smaller in thickness than the holder117, the largest outer diameter of the centering member 111 is almostequal to the inner diameter of the accommodating groove 19.Specifically, when the centering member 111 is formed of polypropyleneand nylon 6, it is preferable that the holder 117 is 2 mm to 5 mm andthe connecting part 120 is 0.5 mm to 1.5 mm in thickness. However, thethicknesses of the holder 117 and the connecting part 120 are notlimited and may be any values as long as the lock ring 22 may besatisfactorily centered by the elasticity of the connecting part 120 andthe connecting part 120 may be appropriately bent when the pipes areconnected to each other.

In this configuration, the inner circumferential protrusion 116 on thesocket inner side is larger in inner diameter than the innercircumferential protrusion 115 at the middle part. Thus, the socket 13and the spigot 15 can be favorably joined to each other and theefficiency of joining the socket and the spigot can be improved even ina state where the pipe axes of the socket 13 and the spigot 15 are bent.Further, since the hold width 118 is formed in the centering member 111,the hold width 118 is caught by the lock ring 22 when the spigot 15 isinserted, so that the lock ring 22 is prevented from projecting from theaccommodating groove 19 towards the inner side of the socket 13. As aresult, the detachment preventive function can be favorably maintainedand the reliability can be improved. Since the end 121 of the hold width118 on the inner side in the pipe diameter direction protrudes moreinward in the pipe diameter direction than the inner circumferentialprotrusion 116 on the socket inner side while the centering member 111is centered, the lock ring 22 can be prevented more reliably fromprojecting towards the socket inner side when the spigot 15 is inserted.

The centering member 111 is plurally divided along the circumferentialdirection, and the divided parts 119 are elastically pressed by theconnecting parts 120 inward in the pipe diameter direction at least whenthe diameter of the lock ring 22 is expanded. Thus, the lock ring 22 canbe favorably centered. Since the connecting parts 120 are provided in anelastically deformable orientation from the outer peripheral surfaces ofthe divided parts 119 towards the outside, the connecting parts 120 donot fit into a divided gap 122 of the singularly divided lock ring 22shown in FIG. 49. Thus, the orientation of the centering member 111 inthe circumferential direction does not need to be controlled withrespect to the lock ring 22, so that the operation efficiency can beenhanced.

Since the connecting parts 120 are formed so as to extend in arc shapefrom the outer peripheral surfaces of the divided parts 119 and have arelatively simple configuration, the divided parts 119 can besatisfactorily elastically pressed inward in the pipe diameterdirection, and the lock ring 22 can be favorably centered.

In FIGS. 47 to 49, the number of the holders 117 and hold widths 118 ofthe centering member 111 is eight along the circumferential direction,but the present invention is not limited to this. The centering member111 is integrally made of resin, so that the manufacturing cost can bereduced as compared to a known centering member made of rubber, but thepresent invention is not limited to this.

As in the illustration, a portion of the socket 13 closer to the socketinner side than the inner circumferential protrusion 116 is larger ininner diameter than the inner circumferential protrusion 116 on theinner side of the socket 13. In this case, the projection 24 of thespigot 15 can be preferably swung in the pipe diameter direction.However, the present invention is not limited to this configuration, andthe portion of the socket 13 closer to the socket inner side may beconstant up to the inner end of the socket 13 in the same inner diameteras the inner circumferential projection 116.

The following will describe still another embodiment of the presentinvention. A force is not uniformly applied by a water pressure in adeformed pipe such as a bent pipe and a T-shaped pipe of a waterpipeline. In order to prevent a water pipeline from being displaced froma normal position by such a non-uniform force, as shown in FIG. 52, acylindrical liner 125 made of metal is attached between the inner end ofa socket 13 and the distal end portion of a spigot 15, for the purposeof constraining the expansion and contraction and the bending of a pipejoint and obtaining predetermined bending rigidity. The outer diameterand thickness of the liner 125 are equal to those of the spigot 15.

Specifically, an inner circumferential surface 126 is formed in the pipeaxial direction closer to the inner side of the socket 13 than a lockring accommodating groove, on the inner circumference of the socket 13horizontally provided. A tapered surface 127 is formed closer to theinner side of the socket than the inner circumferential surface 126. Thetapered surface 127 serves as a guiding surface whose diameter isreduced towards the inner part of the socket. At a portion connectingthe inner circumferential surface 126 and the tapered surface 127, aconnecting part 128 having an arc-shaped cross section is formed. Theinner circumferential surface 126 and the tapered surface 127 aresmoothly connected to each other by the connecting part 128. An innerend surface 129 is formed in the pipe diameter direction closer to theinner side of the socket than the tapered surface 127.

In this configuration, when the socket 13 and the spigot 15 are joinedto each other, as shown in FIG. 50, the liner 125 is inserted into thesocket 13. Thus, the liner 125 is placed at the bottom of the innercircumferential surface 126 with the central axis parallel to the pipeaxial direction.

Next, as shown in FIG. 51, when the spigot 15 is inserted into thesocket 13, an end surface 130 of the spigot 150 is brought into contactwith an end surface 131 of the liner 125 on the socket opening side in anon-concentric state. The liner 125 moves on the inner circumferentialsurface 126 towards the inner side of the socket 13 by being pushed bythe spigot 15. Since the inner circumferential surface 126 is connectedto the tapered surface 127 via the connecting part 128, the distal endportion of the liner 125 can move smoothly from the innercircumferential surface 126 to the tapered surface 127 without fallingat the corner portion connecting the inner circumferential surface 126and the tapered surface 127. The liner 125 having the distal end portionmoved to the tapered surface 127 rises against the tapered surface 127,with a lower portion 132 at the end of the liner 125 on the socket innerside in contact with the tapered surface 127.

Further, as shown in FIG. 52, the liner 125 is positioned on the axes ofthe socket 13 and the spigot 15 while being pushed by the spigot 15 withan end face 133 on the socket inner side in contact with the inner endsurface 129 of the socket 13. The tapered surface 127 is formed so thatthe liner 125 can be self-aligned and positioned on the axes of thesocket 13 and the spigot 15 when the end surface 133 of the liner 125 onthe socket inner side is in brought into contact with the inner endsurface 129 of the socket 13.

The liner 125 is center-aligned with the axes of the socket 13 and thespigot 15 with the lower portion 132 at the end on the socket inner sideguided by the tapered surface 127. Thus, the liner 125 does not need tobe larger in outer diameter and thickness than the spigot 15 forcenter-alignment, but the outer diameter and thickness of the liner 125can be the same as those of the spigot 15 as described above.

FIG. 53 shows a modification example of the pipe joint shown in FIGS. 50to 52. In FIG. 53, instead of the tapered surface 127 of in FIGS. 50 to52, a guiding surface 134 having an arc-shaped cross-section is formedin the socket 13. The guiding surface 134 is formed so as to be insmooth continuity with the inner circumferential surface 126 of thesocket 13 and have an inner diameter reduced towards the inner side ofthe socket 13.

Similarly to the pipe joint of FIGS. 50 to 52, the liner 125 pushed bythe spigot 15 can move on the inner circumferential surface 126 towardsthe inner side of the socket 13 and be smoothly transferred from theinner circumferential 126 onto the guiding surface 134.

The lower portion 132 of the liner 125 transferred to the guidingsurface 134 rises against the guiding surface 134. Similarly to the pipejoint of in FIGS. 51 and 52, the liner 125 is center-aligned with theaxes of the socket 13 and the spigot 15 while being pushed by the spigot15 with the end surface 133 in contact with the inner end surface 129 ofthe socket 13.

FIG. 54 shows another modification example of the pipe joint shown inFIGS. 50 to 52. In FIG. 54, the inner circumferential surface 126 andthe tapered surface 127 are smoothly connected to each other at aconnecting surface 135 having an arc-shaped cross-section, and thetapered surface 127 and the inner end surface 129 of the socket aresmoothly connected to each other at a connecting surface 136 having anarc-shaped cross-section. The tapered surface 127 and the connectingsurfaces 135 and 136 each have a diameter reduced towards the inner sideof the socket 13. Radius R1 of arc of the connecting surface 135 islarger than radius R2 of arc of the connecting surface 136.

With this configuration, the liner provided on the inner circumferentialsurface 126 can smoothly move by being pushed by the spigot (not shown).Thus, the liner can be easily center-aligned with the axes of the socket13 and the spigot 15.

FIGS. 55 to 57 show still another modification example of the pipe jointof FIGS. 50 to 52. In the modification example, a liner centering member138 is provided between the inner circumferential surface 126 and theliner 125. The liner centering member 138 leads the liner 125 to thecenter portion of the socket 13 along the pipe diameter direction. Theliner centering member 138 is formed in a cylindrical shape by usingresin such as nylon 6, and an outer peripheral surface 139 of the linercentering member 138 is provided in contact with the innercircumferential surface 126 of the socket 13. As shown in FIG. 57, theliner centering member 138 includes a plurality of projections 141integrally formed along the circumferential direction on the innercircumference of a thin tubular member 140. Thus, the liner centeringmember 138 is lighter in weight than in a case where the overallperiphery of the liner centering member 138 is uniform in thickness.

The outer peripheral surface 139 may be attached to the innercircumferential surface 126 to fix the liner centering member 138 on theinner circumferential surface 126. The cylindrical liner 125 has anouter peripheral surface 142 supported by the liner centering member138.

The liner 125 supported by the liner centering member 138 is pushed bythe spigot 15 to move to the inner side of the socket 13, so that thelower portion 132 is brought into contact with the tapered surface 127.The liner 125 rises against the tapered surface 127 with the lowerportion 132 in contact with the tapered surface 127, and is self-alignedas shown in FIG. 56. Thereafter, the end surface 133 of the liner 125hits against the inner end surface 129 of the socket 13.

With this configuration, since the liner 125 is supported by thecentering member 138, the moving distance of the liner 125 in the pipediameter direction is shortened during aligning, so that the aligning isfacilitated. The liner 125 moved by being pushed by the spigot 15 isrestricted and prevented from falling by the centering member 138.

The liner 125 can be inserted into the socket 13 after the linercentering member 138 is attached to the inner circumferential surface126 of the socket 13, but the present invention is not limited to this.For example, after the liner 125 is inserted into the socket 13, thecentering member 138 can be attached by being inserted into a gapbetween the liner 125 and the inner circumferential surface 126.

FIG. 58 shows a modification example of the liner centering member 138.A liner centering member 138 of FIG. 58 is singularly divided such thatthe liner centering member 138 includes a tubular member 140 along thecircumferential direction which is partly cut out. Reference numeral 148denotes a singularly divided part. The liner centering member 138singularly divided in this way is elastically reduced in diameter andeasily inserted to the inner circumferential surface 126 of the socket13. When the outer diameter of the liner centering member 138 is set insuch a natural state that the liner centering member 138 elasticallysticks to the inner circumferential surface 126 of the socket 13, theliner centering member 138 does not need to adhere to the innercircumferential surface 126 of the socket 13.

The liner centering member 138 is not limited to the above-describedconfiguration. Specifically, the liner centering member 138 may have,for example, a half-arc-shaped or less-than-half-arc-shapedcross-section, as long as the liner centering member 138 supports thelower portion of the liner 125.

FIGS. 59 and 60 show still another modification example of the pipejoint shown in FIGS. 50 to 52. In the modification example, a thinannular guiding member 145 is provided at the peripheral edge portion ofa part of the liner 125 in contact with the spigot 15.

The guiding member 145 integrally has a cylindrical portion 146 fittedand fixed onto the end of the liner 125 and a tapered portion 147provided so as to project from the liner 125. The guiding member 145 maybe composed of, for example, a resin molded article.

In this configuration, first, the liner 125 is provided horizontally onthe inner circumferential surface 126 of the socket 13, as shown in FIG.59. In this state, when the spigot 15 is inserted into the socket 13,the liner 125 is pushed by the spigot 15 to move to the inner side ofthe socket 13. The lower portion 132 on the socket inner side risesagainst the tapered surface 127 of the socket 13 and is center-alignedwith the socket 13, and in this state the end surface 133 of the liner125 is brought into contact with the inner end surface 129 of the socket13.

At this point, the distal end portion of the spigot 15 is guided by thetapered surface 147 of the guiding member 145 to enter the guidingmember 145. In other words, the guiding member 145 covers the distal endportion of the spigot 15. Conversely, due to the entering of the spigot15, the end of the liner 125 on the socket opening side with the guidingmember 145 attached thereto rises against the spigot 15. Thus, the endof the liner 125 on the socket opening side is center-aligned with thespigot 15, and the end surface 130 of the spigot 15 is brought intocontact with the end surface 131 of the liner 125.

With the above-described configuration, the liner 125 is center-alignedwith the socket 13 and the spigot 15.

FIGS. 61 to 65 show a mechanical-type detachment preventive pipe jointaccording to another embodiment.

As shown in FIG. 61, a flange 80 is integrally formed on the outerperiphery of the opening part of a socket 72 formed at the end of onepipe 71 made of ductile cast iron, and a tapered sealing materialpressing surface 150 is formed on the inner circumference of the openingpart of the socket 72. The tapered sealing material pressing surface 150has a diameter expanded gradually towards the opening end of the openingpart of the socket. An annular sealing material 77 made of rubber isfitted onto a spigot 74 formed at the end of another pipe 73 made ofductile cast iron, and the sealing material 77 is disposed between anouter peripheral surface 151 of the spigot 74 and the sealing materialpressing surface 150.

A push ring 152 as an annular member is fitted onto a part of the spigot74 outside the socket 72. The push ring 152 may be made of ductile castiron as in the pipes 71 and 73 and formed in a continuous annular shapein the circumferential direction. Alternatively, the push ring 152 maybe divided in an appropriate number along the circumferential direction,and the divided parts may be joined to each other by a bolt or the like.

A flange 153 is formed over multiple points of the push ring 152 alongthe circumferential direction. Across the flange 153 of the push ring152 and the flange 80 of the socket 72, a fastening element 154including a T-head type bolt 81 and a nut 84 is disposed in the pipeaxial direction. The fastening element 154 provided across multiplepoints of the push ring 152 along the circumferential direction isoperated, so that the sealing material 77 can be pressed against thepressing surface 150 by a pressing part 155 of the push ring 152. Thus,the sealing material 77 can be compressed between the pressing surface150 and the outer peripheral surface 151 of the spigot 74 to exhibitdesired sealing properties.

In addition to the above-described flange 153, a press clawaccommodating portion 156 is formed over other multiple points of thepush ring 152 along the circumferential direction. An accommodatingrecess 157 is formed on the inner circumferential part of the push ring152 in the press claw accommodating portion 156. In the accommodatingrecess 157, a press claw 158 is accommodated which is formed of ductilecast iron with a constant length along the circumferential direction.

The press claw 158 includes double ridge type claw portions 159 a and159 b formed in the inner circumferential portion of the press claw 158.The claw portions 159 a and 159 b are formed away from each other in thepipe axial direction. As a result, an inner circumferential surface 160is formed between the claw portions 159 a and 159 b in a directionparallel to the pipe axis. A tapered surface 161 is formed in the outerperipheral portion of the press claw 158. The diameter of the taperedsurface 161 is gradually reduced with distance from the socket 72.Reference numerals 162 and 163 denote the end surfaces of the press claw158 along the pipe axial direction.

Reference numeral 164 denotes a press bolt which may be also made ofductile cast iron. The press bolt 164 is screwed into the push ring 152along a direction orthogonal to the tapered surface 161 of the push claw158, so that the tapered surface 161 can be pressed inward along thepipe diameter direction by the distal end of the press bolt 164.

On the outer peripheries of the pipes 71 and 73 including the socket 72and the spigot 74, an anticorrosive coating is formed using a Zn—Snalloy sprayed coating or Zn—Sn—Mg alloy sprayed coating. Further, asynthetic resin coating layer is formed on the outer periphery of thealloy sprayed coating.

As shown in FIGS. 61 and 62, an anticorrosive coating 165 is formedusing a sprayed coating also in the inner circumferential portion of thepush claw 158, that is, the claw portions 159 a and 159 b, the innercircumferential surface 160, and the inner circumferential portion ofthe end surfaces 162 and 163. As the anticorrosive coating 165, a Zn—Snalloy sprayed coating or a Zn—Sn—Mg alloy sprayed coating may be usedsimilarly to the pipes 71 and 73. Alternatively, as the anticorrosivecoating 165 of the press claw 158, a Zn—Al alloy sprayed coating may beused. Further, on the anticorrosive coating 165, a synthetic resincoating is applied over the outer surface of the press claw 158. In FIG.62, reference numeral 166 denotes a synthetic resin coating layer formedby the application of the synthetic resin coating. Alternatively,instead of the synthetic resin coating layer 166, a coating layer 167may be formed using heavy coating. The heavy coating includes powdercoating, liquid epoxy coating, and tar epoxy coating.

Alternatively, as shown in FIG. 63, the anticorrosive coating 165 isformed in the inner circumferential portion of the press claw 158 usinga sprayed coating, the synthetic resin coating film 166 may be formed onthe anticorrosive coating 165, and the coating layer 167 may be formedon the outer periphery of the press claw 158 using heavy coating.

Further, as shown in FIG. 64, the anticorrosive coating 165 may beformed over the outer surface of the press claw 158 using a sprayedcoating, and the synthetic resin coating layer 166 or the coating layer167 using heavy coating may be formed over the outer surface of theanticorrosive coating 165.

It is necessary to select such a coating used for forming the coatinglayer 167 using heavy coating that the dried coating layer does notbecome harder than necessary. If the coating layer becomes excessivelyhard, the coating layer becomes brittle accordingly, so that peeling offof the coating layer may occur when a large removal force is applied onthe pipe joint, thereby remarkably decreasing the corrosion resistance.

The sprayed coatings formed on the press claw 158 and the pipes 71 and73 will be specifically described.

First, the Zn—Sn alloy sprayed coating will be described. It ispreferable that the Zn—Sn alloy sprayed coating contains Sn of over 1mass-% but less than 50 mass-% and Zn of the balance.

Since the alloy sprayed coating is obtained by adding Sn to Zn which isthe essential component, the anticorrosive performance can be improvedcompared to a sprayed coating using only Zn. The anticorrosiveperformance may be about the same as Zn-15Al (Zn: 85 mass-%, Al: 15mass-%). In a case where the content of Sn is not more than 1 mass-% orat least 50 mass-%, the anticorrosive performance cannot be actuallyimproved by the addition of Sn.

The Zn—Sn alloy containing soft Sn has an advantage in that a Zn—Snalloy wire can be easily made as a material for spraying. Further, thealloy sprayed coating containing only Zn and Sn does not cause hygienicproblems even when water supply conduits are constructed by the pipes 71and 73.

Next, the Zn—Sn—Mg alloy sprayed coating will be described. It ispreferable that the sprayed coating contains Sn of over 1 mass-% butless than 50 mass-%, Mg of over 0.01 mass-% but less than 5 mass-%, andZn of the balance.

Also in this case, the anticorrosive performance can be improvedcompared to the sprayed coating using only Zn. The anticorrosiveperformance can be the same as or greater than Zn-15Al (Zn: 85 mass-%,Al: 15 mass-%).

In a case where the content of Sn is not more than 1 mass-% and/or thecontent of Mg is not more than 0.01 mass-%, the anticorrosiveperformance cannot be actually improved by the addition of Sn and Mg.Also in a case where the content of Sn is equal to or more than 50mass-% and/or the content of Mg is equal to or more than 5 mass-%, theanticorrosive performance cannot be actually improved by the addition ofSn and Mg.

The Zn—Sn—Mg alloy also has an advantage in that a wire can be easilymade and hygienic problems are not caused, as in the Zn—Sn alloy sprayedcoating.

Next, the Zn—Al alloy sprayed coating will be described. As shown inFIG. 61, the press claw 158 provided closer to the outer side of thesocket 72 than the sealing material 77 does not contact water in thepipe. Thus, the press claw 158 does not cause any hygienic problems evenwhen the Zn—Al alloy sprayed coating is formed.

It is preferable that the Zn—Al alloy sprayed coating contains Al ofover 1 mass-% but less than 30 mass-% and Zn of the balance. Especially,the above-described Zn-15 Al (Zn: 85 mass-%, Al: 15 mass-%) can bepreferably used. In a case where the content of Al is equal to or lessthan 1 mass-% or equal to or more than 30 mass-%, the anticorrosiveperformance cannot be actually improved by the addition of Al.

The above-described alloy sprayed coatings may contain at least any oneof Ti, Co, Ni, and P. That is, the alloy sprayed coatings may containany one or two to four of Ti, Co, Ni, and P. It is preferable that thecontents of the elements are each at least 0.001 mass-% but not morethan 3 mass-%. If these elements are contained in addition to Sn, Sn—Mg,and Al, the amount of Zn is reduced accordingly.

By containing these elements in the alloy sprayed coatings, theanticorrosive performance can be improved. However, in a case where thecontents of the elements are less than 0.001 mass-%, the anticorrosiveperformance cannot be actually improved by the addition of the elements.Also in a case where the contents of the elements exceed 3 mass-%, theanticorrosive performance cannot be actually improved by the addition ofthe elements.

Similarly, since the contents of the elements are low, an alloy wire canbe made without any difficulties and hygienic problems are not caused.

The alloy sprayed coatings may be porous but the anticorrosiveperformance can be further improved by sealing the pores.

Next, a method of forming an alloy sprayed coating will be described.

As a method for forming an alloy sprayed coating on the surfaces of thepipes 71 and 73 and a method for forming an alloy sprayed coating on thepress claw 158, known spraying methods can be adopted. Specifically, theknown spraying methods include a method of performing arc spraying usinga Zn—Sn wire, a Zn—Sn—Mg wire, a Zn—Al wire (only when an alloy sprayingcoating is formed on the press claw 158), or a wire obtained by addingat least any one of Ti, Co, Ni, and P to the alloy, and a method ofperforming spraying using alloy powder instead of a wire.

Instead, the Zn—Sn alloy sprayed coating can be obtained by performingarc spraying using a Zn—Sn wire or a wire obtained by adding at leastany one of Ti, Co, Ni, and P to Zn—Sn alloy as a first wire, and a Znwire as a second wire. Similarly, the Zn—Sn—Mg alloy sprayed coating canbe obtained by performing arc spraying using a Zn—Sn—Mg wire or a wireobtained by adding at least any one of Ti, Co, Ni, and P to the Zn—Sn—Mgalloy as a first wire, and a Zn wire as a second wire. The same appliesto the Zn—Al alloy sprayed coating.

For example, in order to obtain an alloy sprayed coating containingZn-25Sn-0.5Mg (Sn: 25 mass-%, Mg: 0.5 mass-%, Zn: balance, hereinafter,may be expressed the same), arc spraying can be performed using aZn-50Sn-1.0Mg wire and a Zn wire in equal amounts, instead of using twoZn-25Sn-0.5Mg wires.

Thus, the anticorrosive performance can be further improved. Moreover,the amount of a Zn—Sn—Mg wire used can be reduced to half, so that acost required for mixing can be reduced.

It is not clear why the anticorrosive performance can be furtherimproved by adopting such spraying methods, but the improvement can bethought to be due to (i), (ii), and (iii) described below or a synergyeffect of them.

(i) For example, in a case where arc spraying is performed using aZn—Sn—Mg alloy wire and a Zn wire, the Zn—Sn—Mg alloy and Zn aredistributed in the formed sprayed coating. At this point, since theZn—Sn—Mg alloy has a lower potential than the Zn, the Zn—Sn—Mg alloy ispreferentially dissolved out when the Zn—Sn—Mg alloy and the Zn serve asa sacrificial anode. The dissolved Zn—Sn—Mg alloy forms, on the surfaceof the coating, another coating which is relatively stable. Theimprovement of the anticorrosive performance can be thought to bebecause the other coating suppresses the consumption and dissolution ofthe Zn—Sn—Mg alloy and the Zn.

(ii) The improvement of the anticorrosive performance can be thought tobe because the Zn in the coating physically prevents the dissolution ofthe Zn—Sn—Mg alloy, and when the Zn—Sn—Mg alloy is dissolved, thecorrosion product suppresses the dissolution of the Zn.

(iii) The present inventors observed that the porosity of theZn-25Sn-0.5Mg sprayed coating obtained by using two Zn-25Sn-0.5Mg wireswas about 15%. Meanwhile, the porosity of the Zn-25Sn-0.5Mg sprayedcoating obtained by using a Zn-50Sn-1.0Mg wire and a Zn wire in equalamounts was about 12%. That is, since the latter porosity is lower, theanticorrosive performance can be considered to be improved. The lowerporosity may be because different wires in hardness were used such thatthe Zn-50Sn-1.0Mg wire was softer than the Zn wire.

According to the present invention, it is preferable that a Zn—Sn alloysprayed coating or a Zn—Sn—Mg alloy sprayed coating is formed and heatedat at least the eutectic temperature of alloy (198° C.) but less thanthe melting point. Such heating is performed, so that the anticorrosiveperformance can be further improved. This is presumed to be becauseheating is performed at a temperature in excess of the eutectictemperature of the Zn—Sn alloy or the Zn—Sn—Mg alloy to dissolve onlySn, thereby filling minute pores generated in the sprayed coating toprevent electrolytes from entering the coating when the cast iron pipesare buried in the ground.

Therefore, the Sn does not actually dissolve by heating at a temperatureless than the eutectic temperature, and the above-described effectcannot be achieved. Conversely, if the heating temperature is not lessthan the melting point of the alloy sprayed coating, the alloy isfurther oxidized to lose the original anticorrosive performance.

The heating time is not particularly limited but is preferably 1 secondto 60 minutes. When the heating time is shorter than this range,necessary heating is not sufficiently performed.

As described above, the coating layers 166 and 167 are formed after thealloy sprayed coating is formed.

As shown in FIGS. 62 to 64, the coating layer 166 or 167 forms a coatinglayer having high electrical insulation performance on a part of thepress claw 158 on the outer peripheral portion, that is, the taperedsurface 161. Thus, the press bolt 164 and the press claw 158 areinsulated from each other, so that the press bolt 164 and the press claw158 can be prevented from being electrically connected to each other toavoid corrosion due to electrical connection. As described above, whenthe coating layer 167 is formed by heavy coating on the outer peripheryof the press claw 158, electrical insulation can be particularlyfavorably achieved.

In order that the coating layers 166 and 167 may not be damaged toinhibit the electrical insulation when the press claw 158 is pressed bythe press bolt 164, a sheet material may be disposed between the pressbolt 164 and the press claw 158. A sheet material made of metal canreliably prevent the coating layers 166 and 167 from being damaged.Alternatively, a sheet material made of resin can achieve insulationbetween the press bolt 164 and the press claw 158.

When the pipes 71 and 73 are joined to each other, the spigot 74 isinserted into the socket 72 with the push ring 152 accommodating thepress claw 158 and the sealing material 77 externally fitted. Next, thepush ring 152 is fastened to the socket 72 by the fastening element 154,so that the pressing part 155 compresses the sealing material 77 toexhibit desired sealing properties. After that, when the press bolt 164is tightened up, the claw portions 159 a and 159 b of the press claw 158cut into the outer peripheral surface of the spigot 74. Thus, the spigot74 is integrated with the socket 72 by the press claw 158, the pressbolt 164, the push ring 152, and the fastening element 154, to exert adesired detachment preventive function.

When a large removal force is applied between the socket 72 and thespigot 74 in the event of an earthquake, the tapered surface 161 causesthe claw portions 159 a and 159 b of the press claw 158 to forcefullycut into the outer peripheral surface of the spigot 74, therebyresisting the removal force.

In such a case, the distal ends of the claw portions 159 a and 159 b ofthe press claw 158 and the inner circumferential surface 160 may bedamaged, but an anticorrosion effect can be reliably obtained by theanticorrosive coatings of sprayed coatings formed on the pipes 71 and 73and the anticorrosive coating 165 of a sprayed coating formed on thepress claw 158. For example, when the distal ends of the claw portions159 a and 159 b cut into the outer surface of the spigot 74 with a largeremoval force applied, the coating layer on portions into which thedistal ends cut peels off, and then the portions generally corrode tocause water leakage due to the perforation corrosion of the pipe walland inhibit the desired detachment preventive function. However,according to the present invention, since anticorrosive coatings ofsprayed coatings are formed on the pipes 71 and 73 and the press claw158, even when the coating layer peels off, the anticorrosive coatingsimpede the progress of corrosion.

In the above description, the anticorrosive coatings of sprayed coatingsare formed on both the pipes 71 and 73 and the press claw 158. Accordingto the present invention, the anticorrosive coating 165 has only to beformed on at least the press claw 158. The pipes 71 and 73 may have, forexample, the above-described coating layer formed by heavy coatingrather than a sprayed coating, as long as the coating layer exhibits adesired anticorrosive performance.

On the push ring 152, a highly anticorrosive coating layer can be formedby powder coating or epoxy resin coating to prevent the corrosion of thepush ring 152. As a result, it is possible to reduce the amounts of theanticorrosive coating 165 of a sprayed coating on the press claw 158 andthe anticorrosive coatings of sprayed coatings on the pipes 71 and 73,serving as a sacrificial anode for anticorrosion.

FIG. 65 shows a modification example of the press claw. On a press claw168 of FIG. 65, as on the above-described press claw 158, an outerperipheral surface 169 is formed which has a semicircular transversesection, instead of the tapered surface 161. A claw portion 159 has asingle ridge.

In this case, when a large removal force 170 is applied between thesocket 72 and the spigot 74, the removal force acts such that the pressclaw 168 rises up from the state of FIG. 65. Thus, the claw portion 159significantly cuts into the spigot 74 to exert a desired detachmentpreventive function.

Also in this case, on the inner circumferential part of the press claw168, that is, on and around the claw portion 159, an anticorrosivecoating 165 of a sprayed coating is formed to exert the sameanticorrosive function.

In the above description, the press claw accommodating portion 156 andthe accommodating recess 157 are formed on the push ring 152 as aseparate annular member from the socket 72. However, instead of thisconfiguration, the press claw accommodating portion 156 and theaccommodating recess 157 may be formed on the inner circumference closerto the opening side of the socket 72 than the accommodating portion ofthe sealing material 77 on the socket 72, the press claws 158 and 168may be accommodated in the press claw accommodating portion 156 and theaccommodating recess 157, and the press bolt 164 may be screwed in fromthe outer surface side of the socket 72.

As described in Japanese Patent Application Laid-Open No. 2009-138737 ofthe present applicant, when a pipe for a detachment preventive pipejoint having an annular projection on the outer periphery of the distalend of a spigot is cut to have a desired length, the socket of anotherpipe having a socket-spigot structure is joined to the end of the cutpipe. An annular projection for detachment prevention is formed on theouter periphery of the spigot of the other pipe. When the total lengthof the cut pipe and the other pipe is the above-described desiredlength, a pipe can be configured which is shorter than a standard lengthwith the same detachment preventive function as a pipe having thestandard length. In this case, according to the present invention, theend of the cut pipe and the socket of the other pipe can be joined toeach other with the detachment preventive structure having theabove-described press claw of the present invention.

Results of a corrosion test actually conducted will be described.

Experimental Examples 1, 2

The detachment preventive pipe joint of FIG. 61 was used which includesthe pipes 71 and 73, the push ring 152, the press claw 158, and thepress bolt 164 all made of ductile cast iron. The pipes 71 and 73 had anominal diameter D of 75 mm. A Zn—Sn—Mg alloy sprayed coating was formedwith a thickness of about 50 μm on the outer peripheries of the pipes 71and 73. After filling the pores of the coating, a synthetic resincoating layer was formed with a thickness of about 100 μm on the outersurface of the coating.

As shown in FIG. 62, the Zn—Sn—Mg alloy sprayed coating 165 was formedwith a thickness of about 50 μm on the inner circumferential part of thepress claw 158, the filling of the pores was performed on the coating165, and the synthetic resin coating layer 166 was formed with athickness of about 100 μm so as to cover the entire outer surface of thepress claw 158 including the alloy sprayed coating 165 (ExperimentalExample 1).

Further, instead of the synthetic resin coating layer 166 ofExperimental Example 1, an epoxy resin powder coating layer which wasthe coating layer 167 obtained by heavy coating was formed with athickness of about 300 μm, so as to cover the entire outer surface ofthe press claw 158 including the sprayed coating 165 (ExperimentalExample 2).

Electrical insulation was provided between the press bolt 164 and thepress claw 158 by the coating layers 166 and 167 or by interposing aninsulating sheet between the press bolt 164 and the press claw 158 asnecessary.

In the detachment preventive pipe joints of Experimental Examples 1 and2 thus obtained, as described above, when the pipes 71 and 73 had thediameter D [mm] and a removal force of 3D [kN] was applied to the jointportion, the coating layer 166 or 167 obtained by coating and thesprayed coating 165 peeled off on the claw portions 159 a and 159 b ofthe press claw 158, but peeling-off was not found on other portions.

After the removal force of 3D [kN] was applied in this way, a cycliccorrosion test (by means of Society of Automotive Engineers of Japan,Inc. (antifreezing agent to be tested), JASO M609, 610) was conducted onthe pipe joints of Experimental Examples 1 and 2. Specifically, a cycleof the following conditions was repeated.

(1) salt spray (two hours, 35±1° C., 5% NaCl solution)

(2) dry condition (four hours, 60±1° C., 20 to 30±5% RH)

(3) wet condition (two hours, 50±1° C., >95% RH)

After the test had been continued for four months, red rust was notobserved with the naked eye on the press claw 158 and the claw portions159 a and 159 b, and on the pipe 71 near the press claw 158 in both ofthe detachment preventive pipe joints of Experimental Examples 1 and 2.

Experimental Example 3

Compared to Experimental Example 1, the Zn—Sn—Mg alloy sprayed coating165 was formed with a thickness of about 50 μm on the innercircumferential part of the press claw 158 as shown in FIG. 63, sealingwas performed on the coating 165, and the synthetic resin coating layer166 was formed with a thickness of about 100 μm on the outer surface ofthe coating 165. Further, on a portion of the press claw 158 where thecoating 165 and the synthetic resin coating layer 166 were not formed,that is, the outer peripheral part of the press claw 158, an epoxy resinpowder coating layer was formed as the coating layer 167 obtained byheavy coating with a thickness of about 300 μm. Other configurationswere the same as those in Experimental Example 1.

Under such conditions, similarly to Experimental Example 1, when aremoval force of 3D [kN] was applied to the joint portion, the coatinglayer 166 obtained by coating and the sprayed coating 165 peeled off onthe claw portions 159 a and 159 b of the press claw 158 but did not peeloff on the other portions. Further, the above-described cyclic corrosiontest was conducted on the pipe joint with a removal force appliedthereto and had been continued for four months. After that, red rust wasnot observed with the naked eye on the press claw 158 and the clawportions 159 a and 159 b, and on the pipe 71 near the press claw 158.

Experimental Examples 4 and 5

Compared to Experimental Example 1, as shown in FIG. 64, the Zn—Sn—Mgalloy sprayed coating 165 was formed with a thickness of about 50 μm soas to cover the entire outer surface of the press claw 158, and thefilling of the pores was performed on the coating 165. Otherconfigurations were the same as those in Experimental Example 1(Experimental Example 4).

Compared to Experimental Example 2, as shown in FIG. 64, the Zn—Sn—Mgalloy sprayed coating 165 was formed with a thickness of about 50 μm soas to cover the entire outer surface of the press claw 158, and sealingwas performed on the coating 165. Other configurations were the same asthose in Experimental Example 2 (Experimental Example 5).

Under such conditions, when a removal force of 3D [kN] was applied tothe joint portion, the coating layer 166 or 167 obtained by coating andthe sprayed coating 165 peeled off on the claw portions 159 a and 159 bof the press claw 158 but did not peel off in the other portions.Further, after the above-described corrosion test had been conducted onthe pipe joint with a removal force applied thereto and continued forfour months, red rust was not observed with the naked eye on the pressclaw 158 and the claw portions 159 a and 159 b and on the pipe 71 nearthe press claw 158.

Comparative Examples 1 and 2

Compared to Experimental Example 1, the press claw 158 did not have analloy sprayed coating formed thereon but had only the synthetic resincoating layer 166 formed with a thickness of about 100 μm thereon. Otherconfigurations were the same as those in Experimental Example 1(Comparative Example 1).

Compared to Experimental Example 2, the press claw 158 did not have analloy sprayed coating formed thereon but had only an epoxy resin powdercoating layer which is the coating layer 167 obtained by heavy coatingwith a thickness of about 300 μm. Other configurations were the same asthose in Experimental Example 2 (Comparative Example 2).

Under such conditions, in both of Comparative Examples 1 and 2, when aremoval force of 3D [kN] was applied to the joint portion, the coatinglayer 166 or 167 by coating peeled off on the claw portions 159 a and159 b of the press claw 158 but did not peel off on the other portions.

However, when the above-described cyclic corrosion test had beenconducted on the pipe joint with a removal force applied thereto, inComparative Example 1, red rust was found on the entire press claw 158in two weeks after the beginning of the test, while in ComparativeExample 2, red rust was found on the claw portions 159 a and 159 b ofthe press claw 158 in two weeks after the beginning of the test.

Comparative Example 3

Compared to Experimental Example 1, a Zn sprayed coating was formed witha thickness of about 20 μm on the outer peripheries of the pipes 71 and73, and a synthetic resin coating layer was formed with a thickness ofabout 100 μm on the outer surface of the sprayed coating. The press claw158 did not have an alloy sprayed coating formed thereon but had onlythe synthetic resin coating layer 166 formed with a thickness of about100 μm. Other configurations were the same as those in ExperimentalExample 1.

Under such conditions, similarly to Experimental Example 1, when aremoval force of 3D [kN] was applied to the joint portion, the coatinglayer 166 peeled off on the claw portions 159 a and 159 b of the pressclaw 158 but did not peel off on the other portions.

However, when the above-described cyclic corrosion test had beenconducted on the pipe joint with a removal force applied thereto, redrust was found on the entire press claw 158 in a week after thebeginning of the test.

FIGS. 66 to 79 show still another embodiment of the present invention.

FIG. 66 shows a mechanical-type pipe joint according to the embodiment.The pipe joint has the same configuration as that of the pipe jointhaving a detachment preventive function or earthquake-proof functionshown in FIGS. 30 and 40. The present embodiment is applicable to theslip-on type pipe joint shown in FIG. 1.

In the pipe joint of FIG. 66, an inner circumferential protrusion 175 isformed between a sealing material accommodating portion 75 and a lockring accommodating groove 76. The inner circumferential protrusion 175protrudes inward along the pipe diameter direction and is formed overthe periphery of a socket 72 to form the lock ring accommodating groove76. As shown in FIGS. 66 and 67, in a proper position along thecircumferential direction of the inner circumferential protrusion 175,an arc-like cut-out portion 176 is formed to have the lock ringaccommodating groove 76 communicating with the opening side of thesocket 72. The end of a sealing material 77 on the socket inner side isplaced between the inner circumferential protrusion 175 and the openingside of the socket 72 without contacting the inner circumferentialprotrusion 175.

As shown in FIG. 67, a lock ring 82 is an annular member having adivided part 177 at one point in the circumferential direction. On theinner circumference of the end of the lock ring 82 on the opening sideof the socket 72, a tapered surface 178 is formed which expands towardsthe opening side of the socket 72.

A protrusion 83 on the outer periphery of the distal end portion of aspigot 74 is formed at a predetermined distance from the distal endsurface of the spigot 74. In other words, a straight pipe portion isformed between the protrusion 83 and the distal end surface of thespigot 74. A tapered surface 179 is formed on the outer periphery of theprotrusion 83 on the spigot distal end side.

When a compression force is applied in the pipe axial direction to thepipe joint due to an earthquake, the protrusion 83 of the spigot 74 canmove from the position of a lock ring 82 towards an inner end surface 21of the socket 72. Further, when a tensile force is applied to the pipejoint, the protrusion 83 is engaged with the lock ring 82 from the innerside of the socket 72, so that the spigot 74 can be reliably preventedfrom being detached from the socket 72. Thus, the pipe joint as in theillustration is provided with an earthquake-proof function.

When the socket 72 of one pipe 71 and the spigot 74 of another pipe 73are joined to each other, the lock ring 82 is maintained to elasticallyhave an expanded diameter such that the protrusion 83 of the spigot 74can easily pass through the lock ring 82. Thus, a spacer 180 is used tomaintain the lock ring 82 to elastically have an expanded diameter. Thefollowing will describe the spacer 180.

As shown in FIGS. 68 to 74, the spacer 180 is made of a synthetic resinsuch as polycarbonate, and integrally includes a handle 181 and amaintaining portion 182 for maintaining the diameter of the lock ring 82in an expanded state. The maintaining portion 182 can be freely insertedinto or removed from the socket 72 through the opening of the socket 72,and can be interposed between two end surfaces 183, 183 in thecircumferential direction of a lock ring constituting member at thedivided part 177, shown in FIGS. 67 and 70, of the diameter-expandedlock ring 82 accommodated in the lock ring accommodating groove 76 ofFIG. 66. The lock ring 82 is maintained to elastically have an expandeddiameter with the maintaining portion 182 interposed thus. The spacer180 can be passed through a gap between the socket 72 and the spigot 74and be removed out of the socket 72 when the spigot 74 is inserted intothe socket 72.

The maintaining portion 182 is formed in an arc shape corresponding tothe cut-out portion 176. As shown in FIGS. 68 to 74, on two sideportions of the maintaining portion 182 along the width direction, thatis, the pipe circumferential direction at the distal end of themaintaining portion 182, insertion grooves 184 are formed in the pipeaxial direction. The insertion grooves 184 are opened at the distal endportions of the maintaining portion 182 and the lateral side portions inthe width direction thereof. Thus, the maintaining portion 182 includesa pair of guiding surfaces 185 a and 185 b facing each other in thethickness direction, that is, the pipe diameter direction, regulatingsurfaces 186 constituted by the end walls of the insertion grooves 184,and groove bottom surfaces 187.

When the maintaining portion 182 of the spacer 180 is inserted into thedivided part 177 of the lock ring 82, the two end portions of theconstituting member of the lock ring 82 at the divided part 177 of thelock ring 82 are fitted into the insertion grooves 184, as shown inFIGS. 69 and 74. When the two end portions of the constituting member ofthe lock ring 82 are fitted into the insertion grooves 184, theregulating surfaces 186 hit against an end surface 188 on the socketopening side of the lock ring 82 to regulate the further movement of thespacer 180 as shown in FIG. 74. As shown in FIGS. 70 and 71, when thetwo end portions of the member at the divided part 177 of the lock ring82 are fitted into the insertion grooves 184, 184 of the spacer 180, thegroove bottom surfaces 187 of the insertion grooves 184 are brought intosurface contact with the end surfaces 183 of the lock ring 82.

The groove bottom surfaces 187, 187 of the insertion grooves 184, 184are parallel to each other. Face-to-face dimension E of the groovebottom surfaces 187, 187 shown in FIG. 69 is set in such a range thatthe diameter of the lock ring 82 can be expanded to allow the protrusion83 of the spigot 74 to smoothly pass through the lock ring 82, and thelock ring 82 can be elastically reduced in diameter and be restored tothe original state when the spacer 180 is removed.

Thickness T of the maintaining portion 182 of the spacer 180 is set suchthat the maintaining portion 182 has a sufficient strength to withstanda tightening force as a reaction force from the lock ring 82 whosediameter is elastically expanded by the spacer 180.

The handle 181 has an annular grip 190 exposed outside from the openingof the socket 72, and a connecting portion 191 connecting the grip 190and the maintaining portion 182. As shown in FIG. 75, a distal endportion 192 of the grip 190 in the pipe diameter direction is locatedmore inward in the pipe diameter direction than the outer peripheralsurface of a flange 80 of the socket 72. The grip 190 is formed like aplate having a hole, and as shown in FIG. 75, can be placed parallel tothe end surface of the flange 80. Width W1 of the connecting portion 191is smaller than width W of the maintaining portion 182. Thickness T1 ofthe connecting portion 191 is smaller than the thickness T of themaintaining portion 182.

Reference numeral 193 denotes the linking portion of the connectingportion 191 and the maintaining portion 182, and the width dimension ofthe linking portion gradually increases from the connecting portion 191towards the diameter-expanded maintaining portion 182.

As shown in FIGS. 76 to 78, the maintaining portion 182 of the spacer180 can pass by the cut-out portion 176 of the inner circumferentialprotrusion 175 of the socket 72 in the pipe axial direction and enterthe lock ring accommodating groove 76. The spacer 180 integrally has adisplacement preventive portion 194 formed in accordance with thedimension of the cut-out portion 176 to prevent the spacer 180 frombeing displaced in the circumferential direction of the pipe when thediameter-expanded maintaining portion 182 enters the lock ringaccommodating groove 76. The displacement preventive portion 194protrudes outward in the pipe diameter direction from the linkingportion 193 in the vicinity of the maintaining portion 182.

The operation of joining the socket 72 and the spigot 74 using thespacer 180 having such a configuration will be described.

Before the pipes 71 and 73 separated from each other are shipped to apiping construction site, as shown in FIG. 67, the lock ring 82 has beenaccommodated in the accommodating groove 76 of the socket 72, and thedivided part 177 of the lock ring 82 along the pipe circumferentialdirection has been aligned with the cut-out portion 176 of the socket72. As shown in FIG. 79, the distal end portion of a scissors-like lockring diameter expansion member 195 is inserted into the divided part 177of the lock ring 82, and the lock ring diameter expansion member 195 isopened, so that the inner diameter of the lock ring 82 is expanded to belarger than the outer diameter of the protrusion 83 of the spigot 74.

In this state, as shown in FIGS. 76 and 77, the maintaining portion 182of the spacer 180 is caused to pass by the cut-out portion 176 of theprotrusion 175 from the opening end of the socket 72 and is insertedinto the divided part 177 of the lock ring 82. Thereafter, the lock ringdiameter expansion member 195 of FIG. 79 is taken off from the lock ring82. Thus, as shown in FIGS. 70 and 75, the lock ring 82 is maintained tohave an expanded diameter by the spacer 180.

At this point, as in the illustration, the two end portions of the lockring constituting member at the divided part 177 of the lock ring 82 areinserted into the insertion grooves 184 of the spacer 180. Thus,misalignment of the spacer 180 and the lock ring 82 is prevented in thepipe axial direction and the pipe diameter direction, so that thediameter-expanded maintaining portion 182 of the spacer 180 can be setat a normal position of the divided part 177 of the lock ring 82 withoutmisalignment.

Further, since the displacement preventive portion 194 of the spacer 180is fitted into the cut-out portion 176 of the protrusion 175, the spacer180 is prevented from being displaced in the circumferential directionwith respect to the cut-out portion 176.

With the spacer 180 set thus to maintain the lock ring 82 in thediameter-expanded state, the pipes 71 and 73 separated from each otherare shipped from a manufacturing facility. While the shipped pipes 71and 73 are transported to a destination where a pipeline is to beconstructed, since the distal end portion 192 of the grip 190 of thespacer 180 recedes more inward in the pipe diameter direction than theouter peripheral surface of the flange 80 of the socket 72, the spacer180 can be prevented from hitting against a foreign matter and beingdamaged or falling off.

Thereafter, the pipes 71 and 73 are joined to each other at the pipingconstruction site. At this point, as shown in FIG. 75, the protrusion 83of the spigot 74 inserted into the socket 72 passes inside thediameter-expanded lock ring 82. At this point, the tapered surface 179of the protrusion 83 and the tapered surface 178 of the lock ring 82interact with each other to allow smooth passage of the protrusion 83.

When the protrusion 83 passes inside the lock ring 82 and reaches theinner side of the socket 72 beyond the lock ring 82, an operator holdsthe grip 190 of the spacer 180, pulls the grip 190 out from the openingend of the socket 72, and pulls the spacer 180 out from the socket 72through the gap between the socket 72 and the spigot 74. At this point,since the insertion grooves 184 have the ends on the inner side of thesocket 72 opened as in the illustration, the spacer 180 can move in thepull-out direction without any troubles. As a result, as indicated bythe virtual line of FIG. 75 and FIG. 78, the maintaining portion 182 isremoved out from the divided part 177 of the lock ring 82. Consequently,the diameter-expanded state of the lock ring 82 is released, and asshown in FIG. 66, the lock ring 82 is elastically reduced in diameterand is pressed against the outer periphery of the spigot 74.

After the spacer 180 is removed out thus, as shown in FIG. 66, thesealing material 77 and a push ring 78 are moved along the outer surfaceof the spigot 74 to a predetermined position, and a bolt 81 and a nut 84are tightened up. Thus, the push ring 78 presses the sealing material77, the sealing material 77 accommodated in the accommodating portion 75seals the joint portion, and the pipes 71 and 73 are joined to eachother. The operation of joining the pipes at the piping constructionsite is completed.

The cut-out portion 176 can be formed at at least one position along thecircumferential direction of the inner circumferential protrusion 175 ofthe socket 72.

In the illustration, only the lock ring 82 is accommodated in the lockring accommodating groove 76 but in addition to the lock ring 82, acentering rubber member 23 of FIG. 1 or a centering member 111 of FIGS.45 to 49 may be accommodated in the lock ring accommodating groove 76.

Having described the invention, the following is claimed:
 1. A pipejoint in which a spigot formed at an end of one pipe is inserted into asocket formed at an end of another pipe, the one pipe and the other pipebeing joined to each other, the pipe joint comprising: a fitting grooveformed on an inner circumferential surface of the socket; and an annularsealing material for sealing a gap between the socket and the spigotover a periphery, the sealing material including a heel part fitted intothe fitting groove, and a bulb part interposed between the innercircumferential surface of the socket and an outer peripheral surface ofthe spigot, closer to an inner side of the socket than the heel part,the bulb part including a first bulb continuous with the heel part, asecond bulb positioned closer to the inner side of the socket than thefirst bulb, and a narrow part present on a boundary between the firstbulb and the second bulb, the first bulb having a first sealing portionformed on an outer peripheral portion of the first bulb, the firstsealing portion being pressed against the inner circumferential surfaceof the socket, the second bulb having a second sealing portion formed onan inner circumferential portion of the second bulb, the second sealingportion being pressed against the outer peripheral surface of thespigot, wherein the second bulb is inclined from the first bulb towardsa pipe center in a natural state before the second bulb is providedbetween the socket and the spigot, an inner diameter of the second bulbis smaller than an outer diameter of the spigot in the natural state,and the second bulb is expansible and contractible in a pipe diameterdirection due to elastic deformation of the narrow part.
 2. The pipejoint according to claim 1, wherein the first sealing portion is pressedagainst an inner circumferential surface of a projection formed closerto the inner side of the socket than the fitting groove.
 3. The pipejoint according to claim 1, wherein the first bulb is smaller inthickness than the second bulb in the pipe diameter direction, and a gapis formed between an outer peripheral surface of the second bulb and theinner circumferential surface of the socket in the pipe diameterdirection.
 4. An annular sealing material used in the pipe jointaccording to claim 1, the sealing material comprising: a heel partfitted into the fitting groove formed in the socket; and a bulb partinterposed between the inner circumferential surface of the socket andthe outer peripheral surface of the spigot, closer to the inner side ofthe socket than the heel part, the bulb part including a first bulbcontinuous with the heel part, a second bulb positioned closer to theinner side of the socket than the first bulb, and a narrow part presenton a boundary between the first bulb and the second bulb, the first bulbhaving a first sealing portion formed on an outer peripheral portion ofthe first bulb, the first sealing portion being pressed against theinner circumferential surface of the socket, the second bulb having asecond sealing portion formed on an inner circumferential portion of thesecond bulb, the second sealing portion being pressed against the outerperipheral surface of the spigot, wherein the second bulb is inclinedfrom the first bulb towards the pipe center in a natural state beforethe second bulb is provided between the socket and the spigot, an innerdiameter of the second bulb is smaller than the outer diameter of thespigot in the natural state, and the second bulb is expansible andcontractible in the pipe diameter direction due to elastic deformationof the narrow part.
 5. The sealing material according to claim 4,wherein an inner circumferential surface and an outer peripheral surfaceof the narrow part form recesses, respectively, in a circumferentialdirection.
 6. The sealing material according to claim 4, wherein anannular recess is formed on an outer periphery of a boundary portionbetween the heel part and the first bulb.